You can not upgrade UT tickets via phone with Disney. I tried the other day and was told because I bought 3rd party I had to call them.
What I had to do through UT was order new ones..mine were etickets and then call back with my new order number, and they would process a refund for my other order,
They did say that if I wasn’t able to buy new without a refund first, they were currently giving 95% refund, Since this was only one ticket, I was able to and they are processing the refund on the first one.