The SC18 doesn't have many tuning options out of the box. The only thing you can change about the suspension is the amount of pre-load by adding or subtracting spacers from the shock body. This will change the ride height and have some effect on handling, but if you want to make big changes you will need to change the shock springs.
To change the springs on your SC18, you will need the Factory Team 1:18 Scale Tuning Spring Kit. This kit will give you two additional tuning options for the front and rear springs on your SC18.
My SC18 has a lot of steering out of the box, so I put harder springs in the front (blue or gold springs) to reduce steering and get more rear traction.
Tune the springs on your SC18! Get the Factory Team 1:18 Scale Tuning Spring Kit