Download and extract the .rar file (using either 7-Zip for Windows or The Unarchiver for Mac).
Place the "CFM Skin 2016 v1.3" folders here:
Documents\Sports Interactive\Football Manager 2016\skins
Create the folder "skins" if it doesn't exist.
Start FM16 and go to Preferences screen and then into the Interface tab.
You should see CFM Skin 2016 v1.3 as option in the skin drop down of the Overview box.
Hit the Confirm button.