In many older homes in the United States, the outlets are of the two-prong variety. Since two-pronged outlets are not grounded, it is essential to replace these receptacles with three-pronged versions. The grounded outlets are safer and more capable of protecting modern electronics like computer equipment, televisions and more.
Turn off the power to the two-prong outlets you plan to replace.
Remove the outlet's cover plate and unscrew the two screws that secure the outlet to the box.
Carefully pull the outlet out of the box, using the top and bottom tabs. Do not touch the sides of the outlet until you test for power.
Test the wires for power, using the voltage tester.
Loosen the terminal screws on the outlet and remove the wires.
Look in the back of the wall box to see if there is a ground wire available. If there is no ground wire, one will have to be run to the wall box, or, you can install a GFCI outlet instead. Also, check the wires to see if they are in good shape. If they need it, cut away the exposed section of wire and use the wire strippers to remove 3/4 inch of new insulation from the ends of each wire. If there is a ground wire or you have run a new one to the box, proceed to Step 7.
Connect the ground wire to the green ground screw on the three-prong outlet.
Connect the black wire to the bronze or dark-colored screw on the side of the outlet.
Connect the white wire to the silver screw on the side of the outlet.
Tighten down the other two screws on the outlet and wrap electrical tape around the terminals.
Push the outlet carefully back into the box and secure it in place, using the top and bottom screws.
Install the outlet cover plate and turn the breaker back on.
Test the three-prong outlet for ground by placing one probe of the tester in the hot slot and the other in the ground slot. The tester should read at or about 120 volts.