You take off the whole plastic plinth:
two screws at the very back. One on top, one underneath. The top one is a pig because the seat back gets in the way.
Then at the very front, there's a nut. You get at it from underneath the seat. Put the seat all the way up, and use a torch and mirror to see it. About 10mm AF socket from memory.
After that there's some sort of clips that just take a 'wiggle' to release.