Please note that for events there may be a cancellation fee. Each event should have a section indicating what this fee will be, as well as any conditions. Note also that after a certain date, there may no longer be any refunds due to binding costs with the venue. This is usually considered on a case by case basis.
Registrations may be transferred to another participant, in which case you will need to contact the event organizer directly.
For more specific information about the refund policiy that applies to a given event, check out its refund policy that should be stated on the event's page.