You can only get 2.1. To get 2.2 you would have to root your phone, which will turn it into a brick if you get it wrong. To update the phone, Go to>Settings > About phone> System software updates and then click,Check now.
Another option would be to upgrade your phone. I upgraded to an Htc Desire. It has 2.2 and loads more extra features and non of the problems the Hero had.