Take the seat off.
The 'C' spanner in the toolkit locates in the rectangular slots in the shock absorber, immediately above the spring.
If you look carefully, there are numbers stamped above each slot.
To adjust, fit the spanner in a suitable slot and turn the top section of the shock.
What you are actually doing is altering the preload on the spring.
If you are on the softest setting and can't turn the spanner, try turning the other way. You won't be able to turn it from the softest, straight to the hardest setting.
Hope that helps
