Hi there, Lisa! Thanks for bringing your question to planDisney!
You'll be glad to know that you can most certainly change the date of your
theme park reservation. However, in order to do so, you must cancel your current reservation and make a new one. So, it's really important that you check to see if there is theme park reservation availability for the new date you want before you cancel any current reservations. You can do this by checking
theme park reservation availability calendar. Since you have Park Hopper tickets, you'll want to make sure to click the Park Hopper Tickets button when viewing the calendar.
Another thing to keep in mind is the tier of ticket you have if you purchased a one-day ticket. Certain tier tickets are only able to be used on certain days. This
FAQ page lays out all the days that are blocked out for all ticket tiers.
I hope this helps. Have a magical day!
-Linda