Carefully lift the mainboard. Start on the right sight by lifting it up gently about half an inch. Take your time!

When lifted up, pull it slightly to the right while at the same time gently moving/prying it forth (toward the screen of the PC) and back. The mainboard is 'fixed' mainly through the VGA port, so you might want to check around that area during this process.

Before you finally remove the mainboard, you need to unplug the cable of the LCD screen unit. The cable is attached on the mainboard on the top left (silver plug). Gently pry it out of its silver holder.