How do I remove remove an old through the wall air conditioner?

We just got a new air conditioner to replace our through-the-wall air conditioner, however I am having difficulties removing the old one from it's sleeve. I would like to reuse the old sleeve since it matches our new air conditioner perfectly. I have looked everywhere for screws and removed the only one I could find, but pulling on the "tray" doesn't do anything, it won't even budge. Is there something I am overlooking?