You can reschedule your passes by creating an account here. You can reschedule passes up to 12 hours before your booked time. You will have to create the account with the same email you used to purchase the passes. Be sure to check your email for the confirmation email. 

Once you get logged in, click on your profile icon to see “Your Orders” page. All of your passes will be listed here. The ones you are able to reschedule will have a “Reschedule” button next to them. You can reschedule for any other operational day this season, provided there is still availability. 

See a full set of steps to create an account here.