http://usmanalitoo.blogspot.de/2014/08/How-to-Uninstall-Avast-Antivirus.html. How to Uninstall Avast Antivirus on Windows XP/7/8 & 8.1 – Update Aug 2014 – If you want Uninstall Avast Antivirus on Windows XP/7/8 & 8.1 – Download avastclear.exe on your desktop. Run avastclear.exe click yes after your system is reboot. If you installed avast! in a different folder than the default, browse for it after click remove button. one again your system is reboot.