Using a heat gun or a hairdryer heat up the front of the phone a bit to soften the glue on the double sided tape. You might need to heat up the front several times in the process.

Do not heat up the glass too much as you might cause some damage under the front panel, even though most of the most heat-sensitive parts have been removed. If it's too hot to touch, you have heated the glass too much.

This process will likely ruin the rest of the screen, but if you're careful, and possibly first remove the glass pieces with a razor while reheating the glass frequently, it is possible to save the LCD and digitizer for front glass replacement.

Go around the edges with the razor blade, separating the glass and with it the LCD and digitizer off the frame. Using a suction cup might help a little. Remember to help the flex cables fit out of their gaps.