As you work, try not to accidentally power on the phone. If you do, turn the phone off before resuming disassembly.
Place a suction cup near the bottom edge of the display.
Pull on the suction cup with strong steady force.
Press the edge of an opening tool straight into the frame seam near the suction cup until the edge wedges between the plastic frame and the back cover's lip.
Due to tight tolerances, this will take substantial force. Using a new opening tool with an unmarred edge will help with this step.
Do not use metal tools, as they will most likely crack the screen.
Continue sliding the opening tool along the long edge, releasing the clips along the way.
The last clip in the top-left corner near the alert switch is recessed and can be difficult to release. Take your time and use the flat end of a spudger or an opening pick to help.