If you want to make a change to your booking, the first thing you need to do is check if a change can be made. First, you will want to go to My Bookings.

You will then be taken to a page that asks for your booking reference number and the email that you used to make your booking. Enter this information and click "Find my booking" to access all of your booking’s information, where on the right-hand side, you will see the following (if a change is possible):

If you do not see this, then, unfortunately, changes and cancellations are not possible for your booking.