Can you change the date of a fastpass+ without canceling?

[BJSforVols]

I think I know the answer to this, but I want to ask before canceling our fastpasses. We are in Orlando on a last minute vacation and decided to get 3 day hopper + water park tickets. We have 1 day left on our park hopper tickets and had planned/selected fastpass+ for 7/30 at Epcot. We now probably won't go to the parks on 7/30 but will go on 7/31 instead. Is there a way to look for the fastpass+ selections we want on 7/31 before canceling our 7/30 selections? We may try to stick with 7/30 if we can not get the fastpass+ selections we want on 7/31.