Any changes to a vehicle owner's or title holder's information must be reported to the appropriate registering authority within 21 days of the change. There are a few items you'll need to take with you to ensure things go smoothly.

If you are changing your address :

A copy of your identity document (South African citizens). The original and a certified copy of your national ID and your temporary residence permit (foreign citizens). A utility bill, bank statement, or tax certificate to serve as proof of residence. The necessary forms needed (accessible here: https://www.gov.za/services/services-residents/driving/register-motor-vehicle/change-owner-or-titleholder-particulars-for-vehicle).
If you intend to sell the vehicle:

The seller must complete and submit the NCO form to their registering authority. The seller must provide the buyer with the registration certificate. For submission, the buyer must complete the Application for registration and licensing of motor vehicles (RLV). If the vehicle was registered in SA, the buyer must submit the vehicle registration certificate.