Spring tension does not change ride height. Pre load to that spring does.
Set the ride height of your chassis to about 6mm for on road racing. Do not change it to make your body fit or your car will handle like crap! Ride height is a very important tuning adjustment to make a car handle correctly. If you are planning on drifting then you really do not want to raise the ride height, because it could cause you to traction roll.
If you need to adjust the height of the body then do it with the body mounts or by trimming the body. If you need taller body mounts because the ones that you have were cut down, then you should be able to get them pretty cheap at your local hobby shop.