ticket upgrades

We're going to Universal for the first time in December and if we end up loving it (I hope so!), can we upgrade our 2-day park-to-park tickets purchased through UCT to APs? And, if so, how can we do this? We would of course have to actually go to the parks before we decided if we wanted to...

Hi all, I'm going to Disneyland next month for Dapper Days, and originally purchased 3-day park hoppers online back in August. We recently found out we can go a day early, and would like to add an extra day to our tickets so we can enjoy the parks for longer. My understanding is we have two...