Before cancelling a licence we'd very much like to rectify any problems which might be leading you to consider cancelling. Please open a ticket with our technical support team and we will be pleased to put matters right: http://www.whmcs.com/support/
However, if your mind is made up, then please visit https://www.whmcs.com/members/cancel.php and select the license to be cancelled.
As part of the cancellation process we would appreciate if you could take a few minutes to complete the optional survey, as your feedback will help us improve WHMCS in the future.
All cancellations are normally processed within 72 hours.