Replacing switches is also very simple. First shut off the power feeding the switch or switches. Next, find out if the switch is a single pole or a 3-way, a single pole switch will have 2 screws on one side and a ground screw at the top on the same side.

A 3-way switch will have 2 screws on one side, another screw on the opposite side and a ground screw. On single pole switches you will have 2 wires comming out of the wall, put one wire on top and the other wire on bottom, it doesn't matter which wire goes on top or bottom.

On 3-way switches you will have 3 wires comming out of the wall, one of them wires will either go to the light or is the incomming power to feed the switch. You need to figure out which wire that is, ounce you have identified that wire it will go on the black or different colored screw. The other 2 wires will go on the other 2 screws of the same color. Now you have learned how to install single pole switches and 3-way switches.