The previous posters are correct. For expiry MYW tix, they expire within 14 days of the first use. They can not be upgraded past that point.
If, however, you had gone in to Guest Services on the first day of use and asked to upgrade, you would have been able to pay for the difference between what you wanted and what you paid (say the difference between a 7 day MYW ticket and a 1 day MYW ticket).
You will need to buy all new tix for your trip.