Download the skin.
Extract the files (using either 7-Zip for Windows or The Unarchiver for Mac).
Move the folders inside into your skins folder:
Win Vista/7/8/10: C:\Users\<username>\Documents\Sports Interactive\Football Manager 2016\skins
Win XP: C:\Documents and Settings\<username>\My Documents\Sports Interactive\Football Manager 2016\skins
Mac OS X: /Users/<username>/Documents/Sports Interactive/Football Manager 2016/skins
Create the folder "skins" if it doesn't exist.
Start the game and go to Preferences screen and Interface tab.
You should see "Wannachupbrew-Instant Result Light” as an option in the skin drop down of the General options section.
Hit the Confirm button.