To remove the digitizer, insert and move a plastic opening pick to create a gap between the digitizer and screen.

Carefully lift up the digitizer a little bit and insert a plastic opening card to separate the digitizer from the screen.

There are two things to be very careful of. The cable from the digitizer through to the motherboard goes through the top section, and could be damaged.

The tabs on the side of the home button are light rubber, which gives the return spring to the home key. The rubber seems less resistant to the heat gun than the glue, so if you're not careful you will end up with a pool of melted rubber. In any case, with this method of removing the digitizer, you may not save the existing home button.