iFixit

Remove the 1.5 mm Phillips screw near the lower microphone.

Remove the 1.5 mm Phillips screw near the dock connector cable.

Loosen the three large-headed Phillips screws along the volume button side of the iPhone about one half turn.

It is not necessary to completely remove these screws. When reinstalling the display assembly, be sure the washers are closest to the screw head (as seen in the second picture).

Loosen the three large-headed Phillips screws along the other side of the iPhone about one half turn.

Use the edge of a plastic opening tool to gently pry up the display assembly around its perimeter.

Remove the display assembly from the iPhone.

When reinstalling the display assembly, make sure the digitizer and display data cable are completely pulled through the slot cut into the outer case. Otherwise, the digitizer cable will not reach to its socket on the logic board.

Remember to switch the home button from your old display to the new display (in most cases, this is not provided). Also check that the mesh for the speaker hole is present in the replacement; if not, move it over from the old display.

After reassembly, protect your new display from any scratches by installing a new screen protector.