I recently had a break in and faced the replacement of this window. I found the glass for $35 so I thought I would give it a try. I couldn't find any resources in my Haynes manual other than "remove the glass", or anything online. So I finished the repair myself and decided to share my insight.
The inner door liner has to come off so the sliding window can be removed, this is discussed in the haynes or other manuals decently. I had to remove the window from a junk car with no window functionality, what a nightmare. I can't remember if the outer lower sliding window trim needs to come off, I broke the forward mounting point because I didn't realize it was bolted from the inside of the door. Leave it alone for now. The sliding window rubber molding/race can be pulled away from the vertical divider and pushed out of the way to make it easier to move the vertical divider. The vertical divider is fixed in
3 places: 2 nuts on inner door panel frame, and 1 screw which is accessible from underneath the weatherstipping on top of the door. After this vertical divider/race is pushed sufficiently forward (front of car) the new vent glass in its rubber molding can be squeezed into the space. Then just get it snugged into place and start fastening the hardware back into place.