Use a heat gun or an iOpener as a heating tool. This guide explains how to use the iOpener.
Evenly apply heat to the edges of the touchscreen to loosen the adhesive. Continue to Step 3 once the edge of the screen is warm to the touch.
Do not let the iOpener/heat gun remain on one spot for too long. Excess heat can damage the phone.
When reassembling the phone, use the iOpener/heat gun to help the adhesive fuse to the new screen. Heat the screen edges, apply pressure to the screen, and hold the screen in place until it is secure.
As the adhesive loosens, pry up an edge of the screen with a plastic opening tool or an opening pick. A suction cup may also be useful here.
Use an opening pick to hold that edge in place and continue this process around the entire screen, applying more heat as necessary.
Avoid damaging the LCD screen connector while prying along the screen edges. It is located on the left edge of the phone, across from the volume controls.
During reassembly, new adhesive may need to be applied over the old adhesive to properly secure the screen.
Use a plastic opening tool to flip up the lock on the display cable ZIF connector.
Pull the display cable from its socket on the motherboard.
When installing a new display, carefully remove all remaining adhesive from the phone, and clean the adhered areas with isopropyl alcohol (90% or greater) and a lint-free cloth. Install the display using pre-cut adhesive or a strong double-sided tape such as Tesa 61395. Turn your phone on and test your repair before sealing the display in place.