The problem maybe with the two long rods that go from the handle mechanism to the top and bottom latches. On mine I found that the lock nuts on the end of rods had backed off and the outside handles did not provide enough throw to activate the latches. Eventually the inside handle may no longer open the door.
To take off the inside door panel you need to remove the screws from the top and side of the door this will let you pull off the black metal strip that holds the inside panel. You will also have to remove the inside window frame. You can then pull the panel far enough away from the door get to the rod that activate the latch. Adjust the nut so there is no more than about 1/8 inch. Below are some pictures to show what screw need to be removed to get to the inside of the door.
You will need to remove all the screw along the latch edge and the bottom edge.
When you get all the screw out the frame will come off but the window will stay in place

Hope this helps PM me if you need more info