To cancel an attendee's registration (and issue a refund if a payment was made) navigate to the Registration module, and then to the Attendees menu item. From here, browse or search for the attendee profile that requires a cancellation, then open the attendee's profile.
Next, select the "Cancel Registration" button.
You have the option to charge a cancellation fee by entering an amount into the "Cancellation Fee" field. This amount will be deducted from the amount available for a refund. By default, an email will be sent to the attendee alerting them of the cancellation. If you wish to disable that email, you can do so from the Registration Confirmations screen.
When you are ready, select the "Yes, cancel registration" button to complete the cancellation.
If there is a balance available to refund, navigate to the Billing tab on the attendee's profile, scroll down to the "Transactions" section and select the "Refund" button next to the transaction. Follow the prompts to complete the refund.