If you have installed moodle themes or plugins that are not compatible with your version of moodle or are no longer needed, you can remove them completely from your server and database using the following steps.
Log in to your Moodle site as an admin user.
Site administration > Plugins > Plugins overview
Find the theme or plugin you want to uninstall and click the “Uninstall”.
Uninstalling a theme or plugin removes everything in the database associated with the theme/plugin, including theme configuration and plugin settings.
Manually delete the Moodle theme or plugins folder from the server. This step is important because if you don’t remove the folder from the server, the next time you visit the Moodle site administration page, Moodle will detect the folder again and prompt you to install the theme/plugin.
Site administration > Development > Purge Caches
Please don’t forget to clear the cache this is an important step after your changes on Moodle.