Follow these steps if you find that you are unable to change your WordPress theme from the dashboard.
- Make sure you have a default theme installed such as Twenty Nineteen or Twenty-Twenty
- Make the problematic theme the default theme by activating it from the dashboard
- Log into your hosting account cPanel
- Click on the File Manager and you'll be taken to the screen to manage your hosting account file system.
- Alternatively, you can log into your account via an FTP client like FileZilla
- Locate your active theme's folder under public_html -> wp-content -> themes
- Make a note of the folder name and then rename the active theme folder to something from "theme-name" to "theme-name-disable". Anything at all other than the actual name
- Now go to your home page and reload your website. It should be unable to find the active theme folder (since you renamed it) and then fall back to the default theme you installed.
- Now go to Appearance -> Themes and manage your themes.
- Do not forget to go back into File Manager or FTP to change the theme folder name you renamed back to its original name
