About changing owner and or titleholder particulars
Any changes to the particulars of the vehicle owner or titleholder must be communicated to the appropriate registering authority within 21 days after such change on form NCP (Notification of change of address or particulars of person or organisation).
When you sell your vehicle, you must notify your registering authority on form NCO (Notification of change of ownership/Sale of motor vehicle) and the new owner must register the car in their name.