The availability calendar that bffer provides a link for is the one that does not update in real time. To actually try to make a reservation in real time, you have to have a ticket that has a day available for which you do not have a reservation. Yes, indeed, if you cancel a reservation in order to try for a new one, you could wind up failing to get the new one and losing the old one. Nevertheless, it may be worth taking the chance if that calendar shows availability at the park you want to switch to, and availability at the park you're switching from. At least then, if you can't get the park you want to switch to, you may have a good chance to at least get back the reservation you gave up in order to try for it.
As of right now, Epcot appears to be the only park available on both the 24th and the 25th.
As of right now, Epcot appears to be the only park available on both the 24th and the 25th.