if you lift the inside flap you should see a sew or nut at each end of the flap.
Undo the screws or nuts and hold onto the outside part of the letter flap.
It will drop off once the fixing is removed.
As modern letter boxes have a boxing that sits inside the letter box opening then to replace it make sure you buy one with the correct door depth else you will have to adjust the boxing and screw fittings to suit the door thickness.
Replace my UPVC door letter box from silver to gold recently.
Malcolm M, March 2014
