You need to go back and read your popup. The message is to inform you to move to version 7.5 because 7.1 will no longer be supported. You can still get a free version of 7.5 and i've been using it for a few months now. Here's the link. It will tell you all you need to know.
AVG Anti Virus: AVG Anti-Virus Free Edition
No need to find anything else. While you there, you might as well get the free adware removal program they have. It's a real treat and works just as good as Spybot and Ad-aware.