How to uninstall all installed themes in Windows 10?
If you want to delete all the themes you created or downloaded manually, then follow these instructions:
1. Open the menu “Start” and go to “Settings”.
2. Go to “Personalization” and go to the section “Themes”.
3. Click on one of the Windows themes and close System Preferences.
4. Open File Explorer by pressing “Win+E” on your keyboard.
5. Paste into the address bar “%localappdata%MicrosoftWindowsThemes” and press Enter.
6. Select all files and folders.
7. Delete the selected files.