/Sorry you couldn't get a direct answer... that is because there are many variables that go into the answer.
Is the ticket used, or not?
If not, then they should be able to upgrade them to your choice of ticket without problem and you will pay the difference, or receive the difference back, if your new tickets are less.
If so, they will take the cost of the ticket and divide it by the number of days on it, to get the per day price, multiply that by the number of days you have left and apply that amount toward the purchase of your new tickets and you pay the difference.
If you have your receipt of what you paid for the ticket, you should be able to get a ball park figure, if you know the amount of days left or if you haven't used them at all.
If you don't know how many days are left, the only thing you can do is wait until you get to the parks and have the Guest Relations castmembers read them for you and let you know.
Tickets cannot be read over the phone. This is to ascertain that the information you are given is correct and correctly understood, and the only way to do that is to actually scan the ticket.
Only one old ticket may be used toward the purchase of any one new ticket.
SeashoreCM has given you very good advice!!!!
Hope that helps!
