If you have a computer radio you reduce the ATV or EPA percentage which reduces the servo "throws".

If using non computer radio you have to make mechanical adjustments to the linkage which is harder to explain. First thing to try is moving the control rod in on the servo horn (or closer to the output shaft). You can also move the control rod further out on the control horn at the flaps (or other control surface). The overall affect is the same as reducing the EPA.

Good Luck,
Dennis-