It is fairly straightforward - DVLA contact you 3 months before your licence is due to expire with an application for renewal (D46P form). It's the same procedure that you did when you renewed your licence at 70. It lasts for 3 years which means that every 3 years you have to do it again. This is just to make sure that you are still able to drive properly. Therefore you will need to fill in the application form (D46P) and send it to DVLA and if you do not have any medical conditions which would affect your driving, you should receive a new driving licence to last you for another three years, that is, till you are 76, after which you will have to do the same process again if you wish to keep on driving. Note that you do not need to pay anything for the new licence as it is free for 70 plus and if you do not receive the letter from DVLA 90 days before your current licence expires, you can send them the D1 form (application for new licence) instead.
