Not difficult but you need someone outside that can catch the window when pushing it out of the opening. That is after you remove the screws from the interior trim ring flange.
One point or place I had a leak that was very difficult to locate was the propane compartment door hinge. The hinge is located inside the putty tape and leaked thru the hinge mounting rivets. The compartment door frame did not leak but was the hinge. I found it after 2 years of not knowing where water was coming from by gently squirting the hose at various spots on the camper, starting at the bottom and slowly working my way up from the bottom with a trickle coming out the hose. I had someone inside watching for when the leak showed itself.
I'm also president of the leakers association.