Ahoy, Dan!
Thanks for stopping by the Disney Parks Moms Panel - I'm happy to help.
To cancel or make changes to an existing Port Adventure, Spa appointment or Adult Dining reservation, you'll need to visit Disney Cruise Line's
official page and log in to your cruise reservation. (You'll need to have your reservation number handy). Go to the "Planning Center" and click on "My Cruise Activities".
Once you see the days of your cruise listed, click on the day's plans in which you want to make changes. The plans and activities for that particular day will appear, in chronological order. Choose the activity you want to change and you'll see a "Modify/Cancel" option in the upper right corner. Simply click the Modify/Cancel tab to make changes or cancel a scheduled activity.
I hope this helps! If you have any further questions, please let me know.
Have a magical day! - Diane W.