Before beginning, unplug your iMac and lay it on a soft surface as shown.
Stick a suction cup near each of the two top corners of the glass panel.
To attach the suction cups we sell, first position the suction cup with the movable handle parallel to the face of the glass panel. While lightly holding the suction cup against the glass, raise the movable handle until it is parallel with the other handle.
If your suction cups refuse to stick, try cleaning both the glass panel and the suction cup with a mild solvent.
Gently lift the glass panel perpendicular to the face of the LCD enough to clear the steel mounting pins attached along the underside of the top edge of the glass panel.
Pull the glass panel away from the lower edge of the iMac and carefully set it aside.
During reinstallation, be sure to meticulously clean the inside of the glass panel and the face of the LCD as any dust or fingerprints trapped inside will be annoyingly visible when the machine is turned on.
Pull the vertical sync ribbon cable out of its socket on the LED driver board near the top left corner of your iMac.
The vertical sync ribbon cable has a ZIF style end, but the socket has no lock or retaining flap. Simply pull the cable away from its socket toward the optical drive side of the iMac to disconnect it from the LED driver board.