You are able to modify your reservation within our booking portal online HERE.
Once you've clicked the link, please scroll down until you see in Blue words: "Need to access or modify an existing reservation?" Below that, you will see the option to click "Manage My Reservation."
After that, scroll down until you see, in Red, the option to click "Access Reservations Portal to Change Your Reservation"
If you need additional assistance or want to book for a higher priced day, please contact experience@legoland.com and our team will be happy to assist.