Zenbook UX501JW-DS71T

Can someone help me to swap fn button use? Sometimes I want to use them as they are by default and sometimes I want to toggle them so their secondary use becomes the default function.
E.g. If I am watching a movie I want to be able to adjust the volume with just one hand, currently I need one hand to hold "fn" and need a second hand to reach the volume control. Locating the mouse, navigating to the volume slider control then making a fine adjustment just takes too long!!!
Minor thing but still annoying!!
Thanks
Braddersc