Hello, Jennifer!
Welcome to planDisney, it's great to meet you! Four days is a great amount of time to visit the Disneyland Resort, you'll be able to move at a comfortable pace and experience so much magic!
I'm glad you know that visitors to the parks need a
valid park ticket and a
park reservation. It sounds like your planning is going great! Park reservations cannot be modified, but you can cancel them and rebook through the
My Theme Park Reservations page on the Disneyland website. However, making a new reservation is subject to availability so you'll want to check the
Theme Park Reservation Availability calendar before you cancel your existing reservation to book a new one to make sure that the park you want to book is available. This option is definitely a little bit risky, but if there are still reservations available you can do it!
As a safer alternative option, have you considered upgrading your tickets to
Park Hopper Tickets? This would give your party the option to move from your reserved park to the second park after 11:00 AM on the day of your visit. You can upgrade your tickets with a quick stop by the ticket booths outside of Disneyland Park when you arrive. Park hopping at the Disneyland Resort is so easy, it only takes a couple of minutes to walk between the parks! We really love having the flexibility to go between the parks if one feels like it's getting busy, or if there's a ride or show that we really want to do in the park we didn't start in that day.
I hope this information helps you plan your park days, Jennifer! Wishing you safe travels and a magical visit!
Keep moving forward!
Amanda