If you are registered for an event, your plans change and you cannot attend, you can let the organizer know by cancelling your reservation.

• Logon to the website
• Go to the calendar and click the event
• Click 'already registered'
• Click your name
• Click 'cancel registration'

Once you cancel, the first person on the waitlist (if there is one) will be able to attend. It's also a good way to let the organizer know you won't be attending.