Sometimes you need to uninstall your current AntiVirus product. Maybe you are switching to a different AntiVirus product or maybe you are trying to solve a problem by reinstalling you existing AntiVirus product.
Whatever your reason for uninstalling, this can normally be accomplished by going to the Control Panel and running Add/Remove Programs (Windows 2000, XP) or Programs and Features (Vista, Windows7). In case that does not work, the vendors provide some helpful tools to assist you:
GRISOFT provides this for AVG.
Symantec has this for removing Norton.
The McAfee removal tool is here.