First buy your LEDs, they need to be 3528 SMD units, in the colour you desire.
Take your switch

Take off the front by flexing the shell as the back with a small screwdriver

Take out the rubber membrane

Pull out the circuit board so you can work on it

The led is extremely tiny, this is the one for illumination at night

Remove it by pushing a craft knife under it while desoldering one end, then unsolder the other. Scrape some of the lacquer off either side of the pads left so the bigger led can be soldered in place

The trick now is to line up the new led with the hole in the rubber membrane, as it only just fits, then solder on

Make sure the led is orientated with the missing corner facing the center of the board, as it needs the correct polarity, then reassemble the switch















