Note: this would cause a reboot.

To remove GrimeFighter, go into Control Panel → “Add/Remove Programs” or “Uninstall a Program” (different Windows systems call it different things), find “avast! …” in the list of programs. In Windows 7 one would right+click and on the pop-up window click on “uninstall/change”. (Windows 7 is the only version I have here.) On the Avast screen that pops up, click on “Change” and hit “Continue”. The next screen will show you what is currently installed, broken up into three columns: Shields, Tools, and Languages. Under Tools there is a checkbox for GrimeFighter. uncheck that box and hit Continue. After it does activity, including extracting a bunch of files. It will stop and ask if you want to reboot now or later. Generally I prefer to reboot as soon as possible after such changes.

After the reboot, the stub that launches GrimeFighter will no longer be installed. (You can rerun those steps to add GrimeFighter back in at a later date if you so wish.)