Joystick Controller Problem

hi guys, i have a little question. i am using the default mobile joystick in the unity standard assets folder, how can i clamp the touchpad to a specific part of the screen. i do not want touchpad to work on only half of the screen, i want it to work everywhere on the screen except the joystick section. i am new to this forum and this is my first question :) any help will be appreciated :)