If tickets were part of a package, you can drop the individual from the package for a refund. If you are within 30 days of arrival, there will be a $50 change fee.
If the tickets were purchased separately (not in a package), they can be saved and used/upgraded for s future visit. You will need to pay any price difference.
If purchased from a third party, you may be able to get a refund. Contact the vendor to see.