Found this info some time back. Hope it helps.
Source:Supraforums.com.au
1. All work is done from behind seat. Raise headrest to highest position.
2. Carefully remove the plastic plate covering the screws holding the seat belt guide, then remove the two phillips screws.
3. At the base of the backrest cover plate undo the two 10mm dress screws and pull the cover plate upwards and off the frame to reveal the inside of the squab rear. In the pics that follow except for the last one, I had already removed the cover & foam from the headrest in "investigative work" for this how-to.
4. Using sidecutters, remove the two uppermost hogrings closest to the headrest. If you are replacing all the covers, ya might as well remove the rest of the visible hogrings on the back of the squab at this point.
5. Draw aside the seat foam & cover at the base of the shoulder to reveal a 10mm bolt on each side. Remove these. You will note that this bolt holds an inner plastic frame which caps over the shoulder top on each side.
6. Using an upwards and outwards motion; grip the top of the shoulder cover, foam & plastic frame as one; and pop this combination off the top of the squab metal shoulder frame.
7. Two phillips screws will be revealed which hold the plastic slide bar trim plates. Remove these and carefully manouver out the trim plates.
8. On each side of the headrest supports there are two vertical bars held in place by a 12mm nut & 12mm bolt on each side, remove these and voilà !!!