Hi Lisa, welcome to planDisney!
I am so sorry that you have to reschedule your visit to the
Disneyland Resort. The great thing is that you can easily reschedule your
theme park reservation as long as the tickets are not expired! And even if in the worst-case scenario your tickets happen to expire, you still have options! Per
Disney's eTicket Terms & Conditions, any wholly unused, expired Disneyland Resort theme park tickets (except for special event tickets or tickets purchased from a third party), can be applied towards the purchase of a new theme park ticket in equal or greater value to what was paid for the original ticket.
But back to your main question, to update your reservations, you will need to first cancel your current reservations. You can do this by logging in to your
Disneyland Resort account, selecting the "My Disneyland" link, and then clicking the "Ticket and Reservation Details" link. Select the reservations you wish to cancel and click "Cancel Reservation". You'll then be able to select the party members who need to cancel. Once canceled, you can book your new reservations by heading back to the "Ticket and Reservation Details" link and selecting "Make Park Reservations".
I hope this helps, and if you have any other questions, you know where to find us!
See ya real soon!
Jin