isolate your mains water stopcock under sink
then depending on type of tap in the centre of the tap handle is either a plastic screw or push in cap remove that then you'll see a cross head screw remove.
then remove the tap handle may be a bit tight.
there you'll see the valve you'll need a pair of adjustable spanner to remove the valve undo anti clock wise.
get new valve or washer and refit.
it may be a insert with a washer or a cartridge type.
hi-spec plumbing
August 2007