Step One: Rename your Fonts, WTF and Interface folders to Font.saved, WTF.saved and Interface.saved, so that if you want to undo the installation nothing is gone of your old interface.
* Step Two: Unzip the addon pack to either your desktop(or where ever you want to unzip the files.)
* Step Three: Put the interface, and WTF folder in your World of Warcraft directory.
* Step Four: Inside the WTF folder you will see an 'Account' folder. Enter that folder and inside there you will see a folder that says 'YOUR ACCOUNT NAME'. Rename this folder to your log in/account name. Make sure you put your account name in all caps!
* Step Five: Inside the 'YOUR ACCOUNT NAME' folder you will see a 'Your Server' folder. Rename this folder with your servers name.
* Step Six: Inside the 'Your Server' folder there is a 'Your Character Name' folder. Rename this folder with the character you wish to use this UI with.