Not that hard.
Take out the bolt to holds the rear window track.
Then pull the vent window.
Roll the window up and remove it from the rollers.
Unbolt it, and remove crank from the door.
Install in reverse.
Things to note:
You will have to pull the seal in the top of the window opening out partially to remove vent window.
Don't miss the screw at the very top of the door for the vent window.
Make sure you get the vent window in on the correct side of the brace that runs across the door in that area.
It's easier to re-install with two people.