CANCEL REGISTRATION
You can allow attendees to cancel their registration. Go to Setup > Registration > Advanced and check the box next to Allow Attendees to Cancel Their Registration.
Enabling this feature will add a Cancel Registration link to the registration confirmation page.
It will also add a Cancel Registration link to the registration confirmation email.
CHANGE REGISTRATION
If an attendee needs to change their ticket / subevent registration, only the event coordinator can do that.
1. Go to the Attendees Report, search for the person to change, and click on View/Manage.
2. Next, click on Edit Attendee.
3. Then, find the Ticket Type field and click the Modify link to change the ticket.
Please note: changing a ticket or subevent doesn't change the amount charged. If there is a difference and you need to refund, you'll need to go into the Orders report to process a refund.