If circumstances change, you may be able change the date of your visit, within 12 months of the purchase date. You can do this via the My Account Portal.
Please login to the portal using your order number and email address (or by clicking the link on your order confirmation email), select the 'Booking Portal' link and then 'Modify' next to the ticket you need to amend. The portal will show the dates available for your ticket type and number of times this ticket can be further modified.
The complete ticket terms and conditions can be found HERE.