Uninstall AVG8 using click here
During the uninstall when it asks if you want to re-start your computer now - don't restart, let Revo continue, then when it gives you the option to Select All and Delete do so! Let Revo continue, when finished re-start your computer. You will then have a 'clean-slate' to re-install AVG8.
The downloaded version is probably more up-to-date than the CD version.