depending on why its not working this may be the easiest thing to do!!
take the little metal (or maybe plastic) strip out of the front of the handle by pinging it out with a screwdriver. underneath is a screw, un-do it. then with the door open look just inside the door and you'll see a second screw, undo that!!! the door handle will then come off, go to a scrappy and get a spare one and swap the barrells over so you can still use your key in it. put handle back on door and do up the screws. job done.
if that doesn't work or you think its something else come back and ask again!!! i take it it opens from the inside? is it definately the handle or could it be the catch?