Nick, download a copy of the instructions from the link in the quote below. That will give you an understanding of how the system works.
Measure the height of the lower spring as instructed. If it is more than 66mm, which it most likely is, it will be possible to raise the ride height by putting the spacer above the rate riser spring and adjusting the system so that the distance between the lower part of the hub and the triangular plate is 66mm. The difference between the existing height and 66mm will be the gain in ground clearance. I have gained at least 10 mm in ground clearance.
By the way if you have 205/60 R15 tyres fitted talk to your dealer to see if you can safely fit 205/65 R15 tyres. That will give you about another 10mm of ride height.