Hiroshi, setting the wheel rotation is easy. All you have to do is go into the control panel in windows and choose the DFP and set the rotation value that you want.
If you are looking for the button combination to switch between the smaller default and what you set in windows, you can press the bottom left button on the center spoke, the top right button on the center spoke and the right paddle button behind the wheel at the same time and it will change modes.
As for settings though, others have stated the obvious and it is very true. The amount you want the wheel to turn is personal and you should find the setting that works best for you. If you change the wheel rotation, remember that you will most likely have to change the wheel lock in game as well to allow the steering to feel better and more controllable.