How to Replace a Light Switch. You can replace a nonfunctional light switch in a few minutes. But as with any electrical repairs, be sure to make safety your first concern.
Turn off the power to the switch at the main circuit breaker or fuse box. Test by flipping the switch on to make sure the power is off. Tag the circuit box 'Man at Work' or something similar so no one mistakenly turns the power back on while you're working.
With a screwdriver, remove the two screws holding the cover plate and take the plate off. (The cover plate is the piece of metal or plastic covering the switch.)
Remove the two mounting screws holding the switch in place inside the electrical box.
Pull the switch out of the wall. The switch should come out a few inches, exposing the wires.
Remove the screws holding the two wires coming out of the wall to the switch, making sure to tag which wire came from which screw (they are usually color coded) with colored pens and tape.
Take the switch to the hardware store and get another one exactly like it. Ask a salesperson for help if necessary.
Take the new switch home and hold it up to the wall, right side up, so that the word 'off' appears when the switch is in the off position.
Attach the wires to the screws on the switch's back according to the tags you made earlier.
Secure the new switch in the box with mounting screws.
Replace the switch cover.
Turn the main power back on and test your work.