Yes, the pro version should allow you to upgrade at certain times, it will also do "push" updates. Meaning, if there is a very nasty virus found, and they create a definition file for it, they can automatically push it to computers that have avast pro installed, and that are connected to the internet at that moment.
You can also disable the "popups" so that you don't see them when updates happen as well. I think that's even available in the free version, but I don't have a computer with the free version installed with me at the moment. Just search around the forum for disable avast popup messages.
Then again, you can always download the pro version and use it for 60 days and play around with it. You don't have to pay if you don't like it.