Had to do mine earlier this year, if you want to keep the C1 D1 classification if you have it, depends when you past your test, you will need a Doctor to sign you of as fit. I wasn't bothered as can not remember last time I drove a mini bus or a vehicle up to 7.5 tonne, have heard of people losing motor bike qualification.
Take copy of back of old licence as proof of entitlement.
New licence has to be renewed every three years.
Take it this is thread drift.
Regards
Paul