Put the window in the complete up position and then roll it down say 2 turns. Slide the bottom of the glass into the runners and push it down till it stops. Using the holes in the sides of the metal door panel, put in the screws, youll have to roll it down or up to have access to each of them.
This is assuming you have the door panel off and the glass frame off.
I dont reccomend unbolting the runners, that will make it harder.