Hmmm.....it sounds kind of fishy to me.
Do you mean to upgrade your resort reservation package? I've never heard of any type of location like that. As you mentioned, I have heard of Disney upgrading your room, we even got one once when we checked in. And I know that you can ask about paying more for an upgraded room, but that would need to be handled with Disney reservations if ahead of time, or at the check-in desk whey you get there. I wouldn't trust any upgrade that wasn't directly between you and Disney.
[or, I'm not sure if you might mean upgrade your tickets? You can add days or options to tickets at any Guest Relations, and each park has one of those located both inside and outside the entrance gates.]