TimR:
A "Hopper" window is one that is hinged at the bottom and opens outward.
An "Awning" window is one that is hinged at the top and opens outward.
Hopper windows aren't as popular because if you forget to close your windows before a rain or hail storm, you could have a puddle of water on the floor by the time you do it. Awning windows naturally prevent that by shedding water to the outside.
If your glass pane is held in place by putty, your first step is to remove the putty and then remove the glass pane.
Now, putty was popular decades ago before there were high quality caulks. So, what I tell people that are replacing panes in wooden windows that are held in place with putty is to:
1. remove the putty,
2. pull out the glazing points,
3. replace the glass,
4. push the glazing points back in and
5. Use a high quality caulk like Kop-R-Lastic instead of putty, and
6. Paint both the wood and the caulk once the caulk is fully cured.
Now, if these are PVC windows and it doesn't seem obvious to you what is holding the glass panes in, there will almost certainly be a PVC stop molding on the inside of the window frame, which when removed, will allow the glass to be removed. You will have to remove the window screen to access that stop molding, and the seam between the stop molding and the window frame will be so thin as to make you wonder if it actually is a stop molding or a very thin line in the window frame itself. You need a special pry bar to pry that kind of stop molding out. These special pry bars are sold in hardware stores and are typically called called "scraper/lever bar" because their edge is very thin and can be used for scraping, and the tool is made of high carbon steel so it's very strong and works well as a lever too:
http://www.consolidatedgypsum.ca/Adm..._Gallery_1.jpg
The tool shown in the above link is what you need to remove the stop moldings from modern windows. It's chisel end is sharp enough to fit in the very thin seam between the window frame and the window stop molding. These "scraper/lever bars" can be bought any any hardware store or home center for a few dollars.