At home, a short piece of a cutter blade is perfect. Just hold it parallel with the frame and gently push it down. Then you can lift up the corner of the frame. I use a sharp plastic card, it's a bit safer. It's easier if the device is warm, so you can use a hairdryer, but from a distance, 40C is enough because the overwarmed LCD-foil (the upper layer) is very thin and will be damaged.
The secret trick is a few drops of denatured alcohol to the gap. It's neutral and disappears quickly, but temporarily disconnects the adhesive from the plastic. So it is much easier to lift the frame.
