If you are no longer interested in continuing to be the holder of your domain, you can request de-registration via your administrative contact (PCA) who will receive a notification in order to accept or cancel de-registration.
If the de-registration request is cancelled, your domain retains the status it had prior to the request.
In the event that the administrative contact (PCA) accepts de-registration, they will receive another e-mail so that they can confirm de-registration. 10 days after accepting de-registration (if it is not cancelled) it will become effective and the domain name will become available.
More information User Manual.