I've never had the paid version of AVG but I'd imagine your first step would be to temporarily disable the program. This is usually fairly simple but you'd need to search how to do it on the internet as there may be different methods for different versions. Take note of your version first.
After that, just sign in to your Norton Account and download Norton. This is easy and straightforward. When you're happy with Norton, you can uninstall AVG if you wish or alternatively, just leave it disabled. Whatever you do, don't run the two together as there should be only one antivirus on your computer.