Before you begin, discharge your iPhone battery below 25%. A charged lithium-ion battery can catch fire and/or explode if accidentally punctured.
Power off your iPhone before beginning disassembly.
Remove the two 3.4 mm pentalobe screws at the bottom edge of the iPhone.
Opening the iPhone's display will compromise its waterproof seals. Have replacement seals ready before you proceed past this step, or take care to avoid liquid exposure if you reassemble your iPhone without replacing the seals.
Apply a suction cup to the lower half of the front panel, just above the home button.
Be sure the suction cup does not overlap with the home button, as this will prevent a seal from forming between the suction cup and front glass.
If your display is badly cracked, covering it with a layer of clear packing tape may allow the suction cup to adhere. Alternatively, very strong tape may be used instead of the suction cup. If all else fails, you can superglue the suction cup to the broken screen.
Pull up on the suction cup with firm, constant pressure to create a slight gap between the front panel and rear case.
Insert the flat end of a spudger into the gap.
The watertight adhesive holding the display in place is very strong; creating this initial gap takes a significant amount of force. If you're having a hard time opening a gap, rock the screen up and down to weaken the adhesive until you can fit a spudger inside.
While pulling up on the suction cup, twist the spudger to widen the opening between the screen and rear case.
Make sure the battery is disconnected before you disconnect or reconnect the cables in this step.
Use the flat end of a spudger or a fingernail to disconnect the two lower display connectors by prying them straight up from their sockets on the logic board.
To re-attach press connectors, press down on one end until it clicks into place, then repeat on the other end. Do not press down on the middle. If the connector is even slightly misaligned, the connector can bend, causing permanent damage.
If you have a blank screen, white lines on the display, or partial or complete lack of touch response after reassembling your phone, try disconnecting and carefully reconnecting both of these cables and make sure they are fully seated.