To remove the trim panel with the seat belt slider part you slide the seat belt adjuster to the lowest setting.
Then you need to carefully prize out the airbag
badge (plastic
badge at top of trim). Don't worry its not actually anything to do with the airbag, but a cover where there is a screw holding the trim on. The
badge has plastic expansion grips at the back which are delicate and hold it on, so be careful that you don't break these.
Once the
badge is out you can unscrew the trim. Keep the screw safe. Then you need to pull off the trim. It is pretty tightly fitted as it clips into various points. You work gently from the top where the headling is and very carefuly remove it (pull away). Be careful not not to damge the headling. The bottom of the trip has plastic lugs that slide down into the trim below, so once the top and sides are free you lift it up a bit to release it. Don't be tempted to start at the bottom as you'll break these lugs.
Having written
how to do it, it reads a lot more complicated than it is. Just take it carefully, remove the
badge and screw beneath and then pull away carefully.
Hope this helps
Al