As there are several themes (also known as theme packs) available for Windows 7, users end up installing all available themes. If you are bored with a third-party theme, you can easily uninstall/delete in a few steps.

If you like to uninstall/delete a theme in Windows 7, you need to follow a very simple procedure:

1. Right-click on Desktop and select Personalize.

2. Next, right-click on the theme that you want to uninstall/delete and select Delete option to completely delete the theme from your PC.

Note: You can’t delete Windows 7’s default themes by following the above mentioned procedure.

Note:  The Delete Theme does not appear if you're trying to delete the theme currently in use.

via intowindows.com