Avast has released a uninstallation utility, AswClear that allows you to uninstall Avast antivirus 5 completely from your computer.
Here is how to use this tool. Download aswClear5.exe on your desktop. Disable Avast’s Self Defense feature and restart your system in safe mode.
Run AswClear, select your version, browse to installed folder and click Uninstall button and then restart your computer.