Idiot guide to updating sat nav

I know this has been talked about ,but i can’t find what i’m looking for.

My father in law has got a 2 year old garmin c510 and it has never had the maps updated.
I have been onto garmin and put the seriel number in and i dosn’t get me any farther than to buy an udate for europe.

It just needs the uk map updating and i hav’n’t a clue.

Help help help.

Cheers
Tonyb

give garmin support a ring or it might be cheeper to get a newer satnav the tomtom one is only 99 quid at halfords at the moment