Hi Lacey, welcome to planDisney!
Thanks for bringing your question to us. I will do my best to give some insight!
New Year's Eve is one of the busiest days of the year at the
Disneyland Resort. My wife and I attended once many years ago, and it was the most crowded we ever saw the parks! There were moments throughout the day when the parks reached max capacity and Guests were no longer allowed to enter the parks. This was certainly a special unique experience that we can cross off our bucket list. But I mention this because there is certainly a chance that
Disneyland Park could reach max capacity on the day of your visit. The good news is that I just checked the
Theme Park Reservation Availability Calendar and both parks still have full availability. So if you wanted to change your starting park to Disneyland Park, you can still do that.
To revise your
theme park reservation, you will need to first cancel your current reservation. 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 reservation you wish to cancel and click "Cancel Reservation". Once canceled, you can book your new reservation by heading back to the "Ticket and Reservation Details" link and selecting "Make Park Reservations".
If you have any further questions, please do visit us again!
See ya real soon!
Jin