Having had to hunt around a little for my Grandad to get him up to version 7.5 and 7.1 will be discontinued at some point, click here, download the file and follow the instruction to upgrade from 7.1
My excuse was I was trying to get Grandad upgraded without having to go over there, I use Avast at home now, if I'm honestly though mainly cos I love the voice of "Virus database updated" when the PC at home is fired up