They send you the forms 90 days before your 70th birthday. You then have to decide if you want to retain Groups C1 and D1. If you don't, simply apply for your next photocard online. if you do, you need to get application forms D2 and D4, then undertake a medical and an eye test. Best to get this organised ASAP because getting an appointment for a medical can take six weeks. You can get the D2/D4 pack from some post offices or apply for it online: www.gov.uk/dvlaforms