Hold down the iPhone's power button for several seconds until the phone's operating system shuts down. Insert a paper clip into the the tiny hole on the top edge of your iPhone's casing. Push the paper clip into the hole until the SIM card ejects from its slot. Remove the SIM card from the phone.

Remove the two tiny, Phillips-head screws on the bottom edge of your phone on either side of the data connector. Place your iPhone with the screen facing upward on a flat surface. Place an industrial-grade suction cup on the lower section of the screen's surface. Press down on the suction cup and release so the suction cup grips the screen's surface.

Pull on the section cup until the phone's front and rear panels separate from one another. The front panel houses the LCD screen, and the rear panel houses the main circuit board. Tilt the front panel upward and away from the rear panel until the phone's internal components are visible. Carefully lay the two panel's side by side.

Unplug the two LCD ribbon cable from the circuit board labeled "1" and "2." Carefully unplug the small, white ribbon cable labeled "3." Separate the front panel from the back panel completely. Remove the Phillips-head screws from each side of the touchscreen. These screws fasten the screen to the front panel. Use a credit card to pry the damaged screen out of the front panel, and throw the old screen away.

Place the new screen inside the front panel, and reattach the retaining screws to each side of the screen. Reconnect the "3" cable to the circuit board, followed by the cables labeled "2" and "1." Place the front panel on top of the back panel to conceal the circuit panel. Firmly and carefully press down the front panel until it is flush with the back panel. Replace the two Phillips-head screws on the phone's bottom edge, and replace the SIM card