Here's how you can do it:
1. Visit the Thorpe Park website.
2. Log in to your account.
3. Click on "My Bookings".
4. Select the booking that you want to change.
5. Click on "Edit Booking".
6. Select a new date and time for your visit.
7. Pay any additional charges or receive a refund if the new date is cheaper.
8. Confirm the changes.
Please note that there might be some restrictions on changing ticket dates, such as peak periods or certain blackout dates. It is important to check the terms and conditions of your tickets before making any changes.