http://ubuntuhandbook.org/index.php/2016/05/install-ubuntu-tweak-in-ubuntu-16-04/
download ubuntu-tweak
open ubuntu-tweak --> miscellaneous --> natural scrolling: on
http://ubuntuhandbook.org/index.php/2016/05/install-ubuntu-tweak-in-ubuntu-16-04/
download ubuntu-tweak
open ubuntu-tweak --> miscellaneous --> natural scrolling: on