Before you start, turn the light on. Turn off the correct circuit on the consumer unit - the light should go off.
IMPORTANT: Double check the power is off by turning the switch on & off and checking the light doesn’t come on.
Unscrew the screws holding the switch in place.
Carefully pull out the switch & take a photo of the wiring. If you can’t take a photo, make a note or the wires.
Unscrew the terminals & remove the wires to release the switch.
Compare the new switch to the photo of the old one to work out which wires go where. Check the instructions if unsure.
Place the wires in the correct terminals & tighten the small screws to secure.
Check the wires are tight, then carefully push the wires back behind the switch.
Re-attach the switch with the screws, ensuring you tighten each side evenly.
Restore the power at the consumer unit & check the new switch works.