What are you struggling with? Getting the actual backing out of the trim? Take some photos of both the front and back and we can determine what needs to happen.
Although, I know when I retrimmed mine, all that was required was to take trim off door, and then the material section was stuck/stapled to a thin piece of ply. This ply had several plastic 'prongs' (best word I can think of - plastic bolts?) and was held in place my plastic 'nuts' that pushed over the top. It required a bit of effort, but with a screwdriver and some swearing I was able to flick each one off, and then the panel would come off. All that was required then was to take off the stock material, use it as a template to cut the new material to size, then put it back on exaclty the same way it came off. I used some adhesive spray and it worked fine. Just make sure you don't use the same material as a template for each four doors, as I know for mine they differed very slightly and caused problems with fitting properly later.
I'll see if I can find some pics, but I don't think I took any during the retrim. Hopefully it makes sense

ROCK ON
R~R