Does Universal allow you to upgrade your ticket after using a day? We got two free tickets from a sweepstakes, and need a third. We are taking my son to Universal for the first time, and not sure how he will like it, nor are we sure about how much time we will have to be there. But if we buy a one day ticket, get there and he loves it, will they let us just upgrade for a second day rather than purchasing a separate one day ticket if we want to go back?