It's pretty easy to adjust - start off at the softest setting and rev a couple of times stationary... If the revs drop too far when you let off the throtle and then move up to 'settle', or your car simply stalls, then the spring is too soft. Tighten it up a bit and try again - you should be able to get it so theres no drop off...
Now go out and road test it - if you come to a stop and the revs drop off again or it stalls, tighten up a bit more...
If you end up having it too tight, it won't vent nicely and you will hear 'turbo flutter' when you lift off the throttle when changing gear... simplezzz..
There tends to be a large tolerance between too hard and too soft (missus!) so it's not critical!
Good luck and enjoy....
J.