How to restricted users from changing themes in Windows 7
 

You can easily prevent users from changing any theme and wallpaper in windows 7 by following steps below:

1. Click Start.
2. Search field option, type regedit and press Enter.
3. Go to the following registry key: HKEY_CURRENT_USER SoftwareMicrosoft WindowsCurrentVersion Policies Explorer
4. On the right side, click New – DWORD (32) bit Value.
5. Name the new Key as NoThemeTab.
6. Double click the new DWORD and change its value to 1 (one).
7. Reboot computer for the changes to take effect.
8. If want to revert everything and be able to change the theme and wallpaper again, simply delete the NoThemetab key.