How easy is it to lower and raise the ride height. I want to lower it more, but fearing the M.O.T ramp it has to drive on to. So can I lower it and then raise it up again with a c spanner? or do I need spring compressor etc due to pressure on the spring?

 

Depends on the particular design they have used on your collars. Make sure everything is free and well lubricated.
To adjust one way or the other jack the car up and wind the collars an equal number of whole turns.

Beware of going mad. The driveshafts do not like being run at too large an angle in normal driving.
Jacking the car this way will change the other alignment positions from where they were originally set, especially toe angle whichis critical on the Impreza, esp on the rear.
Graham