It was a little while ago that I did mine but from what I recall:
1- I didn't have 4 'screws' at the bottom, there were two 'christmas tree' yellow retaining clips on each bottom corner, these could be seen lying on the ground underneath the door when open.
2 - once you start working round from bottom to top, popping the retaining clips as you do, you should then be able to see how and where the trim starts, ends and is fixed.
3 - don't remove the door! It need to be done with the door open slightly but that does make access to all points quite tricky but not impossible.
Worth noting - some of the yellow retaining clips broke while doing this as needed to use some force to remove the trim and get to the mechanisms. I'd suggest getting a few in if needed ahead of the job, just in case.
Hope that helps and good luck!