Updating electrical outlets
It’s also a good idea to check with your local electrical inspector to make sure that there are no exceptions in the local code that prohibit these types of installations.Ground-fault circuit interrupter outlets prevent accidental electrocution, and code requires them in baths, kitchens, laundry rooms, garages and outdoor locations.Next, remove the wall cover plate and the old receptacle.The third prong on a three-prong receptacle is for grounding.In order to function properly, the ground screw on the receptacle must be connected to a known ground, usually to a ground wire running from the main panel.On older homes, the flexible metal conduit on armored cable is normally used in place of a ground wire.In my experience, if an outlet box is not grounded, it’s usually due to corrosion that has broken the connection or rusted out the metal conduit at some point between the box and the main panel.
In most cases, this work is all you’ll need to do to replace your receptacles.
Fasten the black wire to the dark-colored screw and the white wire to the light-colored screw.
Again, make sure that both wires are on the "line" side.
A further complication to this method of receptacle replacement is that the downstream receptacles will test as ungrounded even though they are protected by the GFCI.
Because of these complications, I would again recommend having a licensed electrician do the work.