If your circuit breaker box has been damaged by fire, electrical surges or impact, then you will need to replace the entire box and not just the interior panel or individual breakers. Replacing the entire box is easier than replacing just the interior elements. However, its installation can require cutting through a finished wall. Be prepared to do some drywall repair.
Locate the main power supply switch and turn it off. Test that all power is off by trying different lights and appliances in the area serviced by the circuit breaker box to be replaced. Once you are certain that all power is off, tape a sign above the switch warning that you are replacing the breaker box so that no one turns the power back on while you are working.
Remove the power cable from the power inlet connector on the existing circuit breaker box. The inlet connector will typically have two screws holding the power in a clamp-like connection. Loosen the screws and withdraw the cable.
Open the door to the circuit breaker box. Remove the screws that hold the interior panel in place. This is the metal panel that acts as a "frame" for the breakers and hides the wires from view.
Using the painter's tape and permanent marker, put a label on each wire where it connects. Label each one according to the original wiring plan, which should be affixed to the interior of the panel door. This plan is also referred to as the "shelter wiring plan." Transfer the wiring plan to the new circuit breaker box. If the existing box no longer has a wiring plan attached, label your wires starting at the upper left and making that wire #1, and the wire beneath it #2, until you have reached the bottom of the left column of breakers. Start at the top of the right column of breakers and begin numbering by continuing counting from the wire at the bottom of the left column. For example, if your last wire on your left column was #10, then the first wire at the top of the right column will be #11.
Disconnect all the wires from the breakers by loosening and removing the conduit connector nuts. Tape the wires back from the breaker box so they will not interfere with the removal of the box and installation of a new one.
Locate the mounting screws or bolts along the exterior of the existing box. If your existing circuit breaker box is set flush into a wall, you may have to remove a 4-inch-wide strip of drywall along each edge of the box in order to access the mounting hardware. Once you can easily reach them, remove the screws or bolts and lift the old box from the wall.
Lift the new circuit breaker box into position and visually check to see if you can use the old mounting holes. If you can, fill the holes with wood filler first before installing the new box using the mounting hardware included. If the mounting holes for the new box do not line up with the old holes, have an assistant hold the box level while you mark the location of the new holes. Drill the new holes only deep enough to start the mounting screws. Hold the box in place and check that it is level before completely setting the mounting hardware in place.
Remove the panel cover of the new box. Carefully reconnect your wires to their circuit breakers. Make sure that the label on the wire goes with the correct breaker. Make sure all the breakers are set to their "on" positions and replace the panel cover.
Reconnect the power cable to the power inlet connector on the new circuit breaker box. Then, remove your sign from the main power supply switch and turn the main power to the box back on.