If you make a redemption that you wish to cancel, you have 30 minutes after confirming the order to do so. The option to cancel can be found at REDEEM >> History. Click on your order, select "Cancel", and the Tickets will be refunded to your account after you claim them in your Inbox. After this 30 minute window expires, the Cancel button will disappear and the order will be considered final and cannot be changed.
An exception to this policy is if you made a redemption but your order has not shipped for some time already. In this case, you may submit a request to cancel your order at this link.