In order to create a unique website with WordPress, you can install a theme and make the customization accordingly. You can download a WordPress theme whether from the official theme directory or from a third-party source like ThemeForest and TemplateMonster. While you can install multiple themes on a single WordPress site, it’s highly recommended to have only one theme on a single website for a security reason. You can delete all themes other than the active one. Including the default WordPress themes like Twenty Twenty, Twenty Seventeen, and Twenty Nineteen. How to delete a WordPress theme that is already installed?
Just like a plugin, there are two ways to delete an installed WordPress theme. The first option, you can delete an installed theme from the theme manager on the WordPress dashboard. The second one, you can delete an installed theme from the file manager of your hosting panel.
How to delete an installed WordPress theme from the theme manager
This is a simpler solution to delete an installed WordPress as you don’t need to login to your hosting panel. First off, login to your WordPress dashboard. Once logged in, go to the theme manager (Appearance -> Themes). On the theme manager page, hover your mouse over the theme you want to delete and click Theme Details. This will open a window that displays detailed information about the associated theme.
On the appearing window, simply click the Delete button on the bottom-right corner.
Please note that you need a have an administrator role to be able to delete (or install) a theme via the WordPress dashboard.
How to delete an installed WordPress theme from the file manager
If you find no Delete button on the detailed window of the theme you want to delete, you can delete the theme via the file manager of your hosting panel. Log in to your hosting panel and open the file manager. Once the file manager opens, go to wp-content/themes folder. Find the folder associated with the theme you want to delete and simply delete it.
In order to prevent your users to install a new WordPress theme, you can add a new function by editing the functions.php file of your theme. You can simply place the following code right after the last line of the functions.php file content.