This minimizes the risk of electric shock, and allows surge protectors to protect your electrical equipment, such as televisions, computers, stereos, and other devices.
The best way to upgrade a two-prong outlet is to install a three-prong outlet that has a continuous electrical path back to the panel.
A surge protector plugged in to an ungrounded outlet will do nothing, and you could fry your new plasma TV. These can only be safely used on a two-prong outlet.
A pig-tail tester will light up on a grounded two-prong outlet if you touch one lead to the smaller slot on the outlet, and the other lead to the screw in the middle of the outlet.
With the circuit energized, touch one end of the tester to the hot wire, which should go to the smaller slot on the outlet, and one end of the tester to the electrical box (see photo below left). Now all you need to do is attach a bare copper wire to the box, and use this as the ground wire for a three prong outlet (see photo below right).