Invert scrolling direction on Dell touchpad in Windows 8

I would like to invert the scrolling on the touchpad for the 2-finger scrolling gesture to 'natural' scrolling (ie fingers down means scroll up and vice versa). I have a Dell Inspiron 14z-N411z, and my touchpad driver is from Synaptics version 15.3.2.1. Unfortunately, there is no option to invert the scrolling in the touchpad driver settings (see photo).




In addition, I have also seen solutions where you can invert scrolling by editing the register, but that was for Alps touchpads and I have not encountered an equivalent workaround for a Synaptics touchpad. I looked through the registers under the Synaptics program, but could not find the one that would correspond to inverted scrolling.

Thanks for your help!