The theme determines a significant part of the design and appearance of your WordPress website. For example, it influences the layout, typography, colors, and the presentation of posts and pages. Depending on the theme, additional custom templates, design options, and features are also available.
You can install WordPress themes directly from the official theme directory or upload them as a ZIP file. After installation, the desired theme must be activated before it is used for the public website.
In this guide, we will show you step by step how to install, upload, activate, and then check a new WordPress theme.
Briefly explained: Open in the WordPress admin area Design → Themes and select the function to add a new theme. You can install a theme from the WordPress directory or upload an existing ZIP file. The theme will only be used for your website after activation.
What is a WordPress theme? #
A theme determines the basic visual structure of a WordPress website.
Depending on the respective theme, it can influence, among other things:
- Layout
- Fonts and Typography
- Colors
- Header and footer
- Navigation
- Display of posts
- Page display
- Archive pages
- Templates
- responsive design
WordPress fundamentally separates the content of a website from essential parts of its visual presentation.
Themes and plugins are not the same #
Themes and plugins fulfill different tasks.
A Theme is primarily responsible for the presentation and layout of a website. A Plugin in contrast, extends WordPress with additional features.
For example, a contact form, a backup function, or an SEO extension normally belongs in a plugin and not in a theme.
In practice, themes can still provide additional features. However, for important functions, you should consider whether they will still be needed after a later theme change.
Where can I find the installed WordPress themes? #
Open in the WordPress admin area:
Design → Themes
There you can see the themes currently available in your WordPress installation. The theme currently in use is marked as the active theme.
Can WordPress have multiple themes installed? #
Yes. Multiple themes can exist in a WordPress installation. However, only one theme is active at a time for the normal display of the website.
Other installed themes remain inactive for now and can be activated or deleted later.
Important: If you are using a child theme, the corresponding parent theme must also remain installed. Do not delete the parent theme in this case.
Install WordPress theme from the official directory #
WordPress allows the direct installation of themes from the official theme directory.
Install a theme via WordPress #
- Log in to your WordPress admin area.
- Open Design → Themes.
- Click the function to add a new theme.
- Search for the desired theme.
- Open the preview or detailed information if necessary.
- Click on the desired theme Install.
- Wait for WordPress to finish the installation.
- Only activate the theme when you actually want to use it.
Search for a specific theme #
If you know the name of the desired theme, you can use the search function. WordPress will show you matching themes from the official directory.
When making your selection, you should not judge by appearance alone. For example, check:
- whether the theme is actively maintained
- whether it is compatible with your WordPress version
- whether it fits your desired website concept
- whether the required layout features are available
- whether it is designed to be responsive
- whether understandable documentation is available
Practical Tip: Do not choose a WordPress theme based on its demo design alone. Regular updates, good performance, clean mobile display, and compatibility with your most important plugins are much more important in the long run.
Use theme preview #
WordPress can offer a preview or detailed view for themes. This can give you a first impression of the design.
You should not expect, however, that your own website will look exactly like a preview image of the theme provider after activation.
Demo websites often use:
- specially prepared content
- certain images
- preconfigured menus
- additional plugins
- Demo imports
- individual settings
The theme provides the technical and design foundation, but not automatically the complete demo website.
Install WordPress theme as a ZIP file #
Not every theme is installed directly via the WordPress directory. With premium themes or custom-provided themes, you often receive a ZIP file.
You can upload these directly via the WordPress admin area.
Upload theme as ZIP file #
- Open Design → Themes.
- Select the function to add a new theme.
- Click on Upload theme.
- Select the theme ZIP file on your computer.
- Click on Install now.
- Wait until WordPress has processed the file.
- Activate the theme afterwards if you want to use it.
Do not unzip the ZIP file before uploading #
If WordPress expects a theme ZIP file, you should usually upload it directly as a ZIP file.
You don't need to unpack them on your computer beforehand and upload the individual files. WordPress unpacks a properly structured theme archive itself during the installation.
„The theme could not be installed“ #
If WordPress reports that a theme could not be installed, you should first check whether you are actually using the correct ZIP file.
For commercial themes, a downloaded complete package sometimes includes additional files such as:
- Documentation
- License information
- Plugins
- Demo files
- the actual theme ZIP file
In this case, the entire download package may not be allowed to be uploaded as a WordPress theme.
Attention: With such a provider package, only extract the outer archive to find the actual installable theme file. The theme ZIP file intended for WordPress is then uploaded again as a ZIP file.
What does „The theme is missing the style.css stylesheet“ mean? #
A well-known error message during theme installation indicates that WordPress could not find the required stylesheet.
A typical message refers to:
style.css
This frequently means that the uploaded ZIP file is not a correctly structured WordPress theme or that you selected the wrong archive from a larger download package.
Therefore, check the theme provider's documentation and the contents of the downloaded package first.
Installing a theme and activating a theme are two different steps #
After installation, a theme is initially only present on the server. It does not yet change your publicly visible website.
Only when you the theme activates, it becomes the active theme of your WordPress installation.
This allows you to install a new theme first without immediately using it for visitors.
Activate WordPress theme #
Activate installed theme #
- Open Design → Themes.
- Search for the desired installed theme.
- Check that you have selected the correct theme.
- Click on Activate.
- Then open your website in the frontend.
- Check the most important pages and features.
Attention: On an existing website, changing a theme can significantly alter the appearance. Therefore, do not activate a new theme unthinkingly on a production website.
What happens during a theme change? #
Your normal WordPress content, such as posts and pages, is generally not simply deleted by switching themes. However, their appearance can change significantly.
Those affected can include, for example:
- Header
- Footer
- Navigation
- Fonts
- Colors
- Page widths
- Sidebars
- Widgets
- Post display
- Archive pages
- Templates
- theme-specific functions
A new theme interprets and designs the existing content according to its own templates and design rules.
Our recommendation: Do not change the theme of an existing website directly on the production installation. If possible, test the new theme in a staging or test environment first, checking not only the homepage, but also navigation, subpages, posts, forms, and mobile display.
Are posts and pages deleted when changing themes? #
Standard WordPress posts and pages are stored in the database and are generally retained when switching themes.
However, that does not mean that everything after will look exactly the same as before. Content or functions that are closely tied to the previous theme can be particularly problematic.
Observe theme-specific functions #
Some themes provide their own functions, shortcodes, blocks, or special content elements.
If your website makes intensive use of such features, switching themes can cause additional customization work.
Therefore, check before switching whether important content depends on the previous theme.
Safely changing a theme on an existing website #
For an already live website, a comprehensive theme change should be prepared.
Before changing the theme #
- Create or check a current backup.
- Check the requirements of the new theme.
- Check compatibility with essential plugins.
- Document important settings of the previous theme.
- Test the change first in a staging or test environment, if possible.
- Check the entire website after the switch.
For an extensive corporate website or an online store, testing outside of the production website is particularly useful.
What should be checked after changing a theme? #
Do not check just the homepage.
A meaningful test includes, among other things:
- Home
- important subpages
- Blog posts
- Blog and archive pages
- Header
- Footer
- Navigation
- Contact forms
- Buttons and Links
- Pictures
- Mobile view
- 404 page
- Search, if used
- Shop pages in WooCommerce
Also check whether important page titles, headings, and structuring elements are still correctly output.
Check menus after a theme change #
A new theme may provide different menu positions or navigation areas.
Because of this, it may be necessary to reassign existing menus to a position or to adjust the navigation in the new theme.
In block themes, navigation is also managed differently than in many classic themes.
Check widgets after changing the theme #
Widget areas are also theme-dependent.
For example, a theme can have sidebars or footer widget areas that the new theme does not provide in the same form.
Therefore, check the sidebar and footer in particular after a switch.
Classic themes and block themes #
WordPress supports different theme concepts.
Classic themes often use traditional PHP templates and can provide features like the customizer, classic menus, and widget areas.
Block Themes are designed for block-based website editing and work with the WordPress Site Editor.
With a block theme, you can find under Design typically the Editor, through which templates, styles, and navigation, among other things, can be managed.
Why is the customizer missing after a theme change? #
When you switch from a classic theme to a block theme, the area can Design significantly change.
The classic WordPress Customizer may not be available in the same form with a block theme.
Many design tasks are handled via the website editor instead. This is not an installation error, but a consequence of the different theme concept.
Install premium theme #
A premium theme is often purchased directly from the respective provider and then installed as a ZIP file.
Depending on the provider, an additional license activation may be required after installation, for example, so that:
- automatic updates
- Premium features
- Template libraries
- Support services
become available.
The exact procedure is determined by the respective theme provider.
Install theme only from a trusted source #
Only install themes from sources you trust. This applies especially to paid themes.
Avoid unofficial copies of commercial themes from unknown download sources. Tampered theme files can pose a significant security risk.
Security principle: Use the official WordPress theme directory or the original source of the respective theme provider.
What is a child theme? #
A child theme is a standalone theme that is based on another theme – the parent theme.
It is primarily used when files or templates of a theme need to be individually customized without writing these changes directly into the parent theme.
This allows individual customizations to be preserved when updating the parent theme.
However, a child theme is not required for every website.
Do not delete the parent theme of a child theme #
A child theme requires its corresponding parent theme.
When a child theme is active, the parent theme must not simply be deleted. WordPress still requires its files as a foundation.
How many themes should you leave installed? #
You don't have to keep every theme you've ever tested.
Typically, you need:
- the active theme
- additionally the corresponding parent theme for a child theme
- where applicable, a current standard theme as a technical fallback
Which themes you should actually keep depends on your website and your maintenance concept.
Why can unused themes be a problem? #
Even an inactive theme consists of files on your server.
If such a theme contains security vulnerabilities and is not updated, it can create unnecessary attack surface.
Therefore, remove themes that you definitely no longer need and keep remaining themes up to date.
Update WordPress theme #
Like WordPress itself and plugins, themes can also receive updates.
Updates can, for example:
- Security fixes
- Bug fixes
- Compatibility adjustments
- new features
contain.
Theme updates should therefore not be ignored permanently.
Attention: If you have modified parent theme files directly, these customizations can be overwritten during a theme update. For permanent file-based theme customizations, a child theme may be the better solution.
Theme cannot be installed #
If an installation fails, there can be various causes.
Check among other things:
- Is the ZIP file a valid WordPress theme?
- Are you using the correct archive from the download package?
- Has the file been completely downloaded?
- Is there enough storage space available?
- Does the server configuration allow the file size?
- Does WordPress have the necessary file permissions?
- Is the theme compatible with your WordPress and PHP environment?
Always record the exact WordPress error message in the event of an error.
Theme upload is too large #
If WordPress rejects an uploaded theme file because of its size, a server-side upload limit may have been reached.
For example, relevant factors can include PHP settings for the maximum allowed upload and POST size.
Do not change such values blindly. If you are hosting on CURIAWEB and cannot upload a legitimate theme file, our support team can check the technical cause.
„Target folder already exists“ #
During a theme installation, WordPress may report that the destination folder already exists.
This can happen, for example, if:
- the theme is already installed
- a previous installation was incomplete
- a theme folder was manually copied to the server
Check first under Design → Themes, whether the theme already exists.
Attention: Do not delete existing theme directories carelessly via the file manager. First, check if the theme is active or required by a child theme.
Theme causes an error after activation #
If an error occurs immediately after activating a theme, there may be an incompatibility with WordPress, PHP, or a plugin, for example.
Note the error message and check whether the error clearly started with the activation of the theme.
For a production website, functionality should first be restored before any further changes are made.
Theme and Elementor #
Elementor is a page builder and not a WordPress theme.
Even a website designed with Elementor still requires an active theme.
The theme provides basic WordPress structures and templates, while Elementor can be used for designing specific content or templates.
Therefore, a theme change can also affect areas of an Elementor website that are not completely controlled by Elementor.
Theme and WooCommerce #
When using WooCommerce, you should ensure clean WooCommerce compatibility when choosing a theme.
After a theme change, check in particular:
- Shop Overview
- Product pages
- Cart
- Checkout
- Customer account
- Mobile view
An visually attractive theme is not automatically suitable for a productive online shop.
Delete theme #
An inactive theme can be deleted via the theme management.
You cannot simply remove the active theme like any inactive theme. First, activate another suitable theme.
With a child theme, you also need to make sure that its parent theme is still required.
Attention: Do not delete any theme if you are not sure whether your website or an active child theme depends on it.
Common mistakes during theme installation #
- falsche ZIP-Datei aus einem Anbieterpaket hochladen
- Demo-Screenshot mit einer fertigen Website verwechseln
- neues Theme sofort auf einer produktiven Website aktivieren
- Theme wechseln, ohne vorher ein Backup zu kontrollieren
- nach dem Wechsel nur die Startseite prüfen
- Navigation und Widgets nach dem Wechsel nicht kontrollieren
- Parent-Theme eines aktiven Child-Themes löschen
- Premium-Theme aus einer unbekannten Quelle herunterladen
- ungenutzte Themes jahrelang installiert und ungepflegt lassen
- Dateien des Parent-Themes direkt verändern
- Theme und Page Builder miteinander verwechseln
Checkliste nach der Installation eines Themes #
Neues Theme kontrollieren #
- Ist das richtige Theme installiert?
- Ist es mit deiner WordPress-Version kompatibel?
- Benötigt es zusätzliche Plugins?
- Ist eine Lizenzaktivierung erforderlich?
- Hast du vor der Aktivierung auf einer bestehenden Website ein Backup?
- Sind Header und Footer korrekt?
- Funktioniert die Navigation?
- Werden Seiten und Beiträge richtig dargestellt?
- Funktionieren Formulare und wichtige Website-Funktionen?
- Stimmt die mobile Darstellung?
- Funktionieren bei WooCommerce Shop, Warenkorb und Checkout?
When should you contact CURIAWEB support? #
Wenn du als CURIAWEB-Kunde ein WordPress-Theme aufgrund eines technischen Fehlers nicht installieren oder aktivieren kannst, kannst du dich an unseren Support wenden.
Hilfreich sind dabei:
- die betroffene Domain
- Name und Version des Themes
- die genaue Fehlermeldung
- ob das Theme über WordPress oder als ZIP-Datei installiert wird
- ob das Problem bei Installation oder Aktivierung auftritt
- what change was made immediately before the problem
Die individuelle Einrichtung, Gestaltung oder Anpassung eines Themes ist dagegen von einem technischen Hosting- beziehungsweise WordPress-Fehler zu unterscheiden.
Summary #
Ein neues WordPress-Theme installierst du unter Design → Themes. Themes aus dem offiziellen WordPress-Verzeichnis können direkt installiert werden. Premium- und individuell bereitgestellte Themes werden häufig als ZIP-Datei hochgeladen.
Installation und Aktivierung sind zwei unterschiedliche Schritte. Erst durch die Aktivierung wird das neue Theme für die öffentliche Website verwendet.
Auf einer bestehenden Website sollte ein Theme-Wechsel sorgfältig vorbereitet werden. Beiträge und Seiten bleiben grundsätzlich erhalten, ihre Darstellung sowie Navigation, Widgets, Templates und themeabhängige Funktionen können sich jedoch deutlich verändern.
Installiere Themes nur aus vertrauenswürdigen Quellen, halte sie aktuell und kontrolliere nach einem Wechsel nicht nur die Startseite, sondern alle wichtigen Bereiche und Funktionen deiner Website.
