AVG's recommended upgrade method is to run the install programme, and use the 'repair' option.

I have found it a breeze on most machines I have upgraded, except for those with Webroot's Spy Sweeper installed. With that you need to disable Spy Sweeper first, but that's not exactly a surprise! If you don't (I didn't!), AVG upgrades okay, but the updates won't work... so you uninstall AVG 7.5, re-start the PC (yawn!!), stop Spy Sweeper (it re-starts on the next reboot, but that's okay), reinstall AVG, and all's well.

AVG's new Anti-Spy software seems quite good (it's something else they bought and re-badged, but I can't just remember what!) - you get 30 days full function, after which you either pay 25 quid for a licence, or you lose some of the functions. Manually updating is probably a bit of a nuisance, but if it saves 25 quid...!!