How to uninstall AVG completely

Just note that many uninstallers are no more effective in removing an application than the app's built-in function - which is what they're using? You need to get an uninstaller that records a snapshot of the the complete install. Some also monitor apps to update the snapshot for changes made by the application such as updates.

Otherwise, you're better off in many cases just using a removal tool by the manufacture, which specializes in removing the app where normal uninstall is not effective.