Rear spring adjustment, How

My rear springs need the pre-load adjusting, from 2 to 4 for a pillion. There is a ring arround the bottom with holes in from 1 to 5 called, yes you got it "pre load setting" no mention in the book of how to doit!!. I tried sticking a screwdriver in and turning it but that didn't work, although I didnt force it.
Thanks.....Rod [smiley=thumbup.gif]

Mine has a small allen grub screw through it to lock it in position. :)

Thanks, I shall have a closer look

Have you got a C-Spanner in the tool kit?