You need to take the inner door skin off. Do that by taking off the handle and window cranks. Then there are 2 bolts that you will need to access by cutting a little X in the plastic so that you can get a socket to the bolt. The window channel on the back side of the vent windo continues down into the door...probably 8-12 inches, but then if you already have the replacements, you know what I am talking about.
Pull those two bolts out, and then there is at least 1, but maybe 2 hex screws on the top of the door frame. Unscrew those, and the tilt the vent window back towards the open area. It should pull right out.
Install is the opposite.
This is the procedure on my 1985. There may be more steps if you have power windows or locks. Mine doesn't.
HTH