Editing the standard FPS to work different

Hello. I recently started making a game, and when trying to test my ingame GUI, i found that the camera would spin wildly when i reached for the menu buttons. I have a little bit of trouble with trying to figure where to edit the mouselook script, but i would like to edit it in such a way, that the mouse only moves the camera when the right mouse button is held. i'm not very good with scripting yet, and would really appreciate any help. the script is the standard MouseLook.cs, which is inside the first person controler.