If you read the form, it will tell you exactly what to do when you sell the
vehicle look at section 6 and the bottom of page 9 - and once the DVLA have
received that information, they will send you a letter of confirmation.
Again, if you merely want to change your name amd address (and not sell the
vehicle), reading the form will tell you what to do - look at section 6 -
it's a common thing to do and it's simple
Have a look at http://www.dvla.gov.uk/ for further information - and this
also applies in Northern Ireland.
Tanner-'op