If you're not having problems with it I'd hazard a guess that you're not the average 'click yes to everything that pops up' kind of user, in which case you don't need to pay for antivirus.
I'd switch over to MSE or Avira and use whichever you like more (bearing in mind you can only run one antivirus, you can't use two or they conflict). Both are free, there's not really any need to pay for antivirus nowadays. It's the illusion of security, free antivirus will do everything a paid for version will do. The problem is people don't know that. The advantage of free AV's is they tend to be very lightweight and won't eat up resources like AVG does.
If you ever have a problem with some program showing up or things feeling slow or popups, first thing to run is Malwarebytes. It's hands down the best anti-malware program there is, fortunately it's free as well.
If you find something Malwarebytes won't get rid of, it'll be spyware. Use Superantispyware and that'll zap 99% of things that aren't 0day.