Basically;
remove third brake light if so equipped.
remove seat side bolsters by removing bolt at bottom (easiest done with rear seat bottom out, two tabs up front, pull and pull seat up and out), lift bolster up and away.
Its been awhile, so my memory is a little fuzzy, so you may have to remove some plastic trim around the c-pilar, jimmy with the shoulder belt and pull the panel out.
Also do a search on this one. You're not the first to ask.