I swapped out my driver side door check a short while ago; due to the horrible racket it was making, when opening and closing the door. Once removed and replaced, the cause of the noise and damage to the door check was evident. It would have snapped the rest of the way, in the not so distant future.
Remove the door panel. Remove the two nuts holding the door check in place and unpin the rod from the door jam. Now you'll have to snake the old unit out, between the window and the window regulator. Replacement is not difficult, but small hands definately help. I replaced mine, with the window in the up position.
Just try to remember how you remove the old one, so the new one can go back in, with less difficulty.....it is tight in there....