Hi Erica!
Yes, you may change your park reservation dates. I switched my reservation dates on our last trip, the trip before, and even in the middle of one of our visits.
First, check the
Theme Park Reservation Availability Calendar. If the parks are green on the days you wish to attend, head over to your
My Disney Experience. You will then need to bring up your original park reservation. The current system does not allow for modifications, so you will have to cancel your first reservation and prepare to make a new one. After canceling your original reservation, hit up the
Disney Park Pass page to make a new one. You will need to complete the process for each date and park you wish to adjust.
Now you are off to pummeling down mountains, traveling at lightspeed through space to
Black Spire Outpost, and enjoying all the Mickey shaped food!
Enjoy your wonderful adventure!
Elisabeth