I recently tried to upgrade my AVG Free Antivirus version 8 to the new 8.5 version. 

I downloaded the new installer and ran it like usual. It appeared to go through the installer OK, however after the final reboot I did not have any Antivirus software loaded. I decided to uninstall whatever version may or may not be installed but got some errors about not able to stop the required windows services. 
What I ended up doing was open up the Computer Management MMC console and set the AVG services to Disabled then reboot. This would prevent the services from starting on the next reboot. After reboot I was able to run the uninstaller again and it ran successfully. 
(NOTE: there is also an AVG uninstaller found at http://www.avg.com/download-tools) 
I then redownloaded the new 8.5 version just to make sure I had a complete and correct install file. The new installer worked correctly and I now have AVG 8.5 Antivirus.
This may not be the only way to fix this problem but “ItFixed It for Me”.
For more “ItFixed it for Me” articles click here.
For my Product Review of AVG Antivirus click here.
Please let me know if anyone else has come across the same problem.