Download the World of Warcraft Interface AddOnKit
Warning: Customising the interface is a very technical endeavor, and you should not attempt it unless you have a good working knowledge of XML and Lua.
There is no official support for modifying the WoW interface. If you experience any issues with the interface after modifying it, you can disable any unofficial AddOns and changes in the AddOns menu at the character selection screen. Blizzard Customer Support cannot assist with setting up any kind of interface modification. However, you can find information for developing or installing add-ons in the UI & Macros Forum on the World of Warcraft website.
If you understand the warning and still want proceed, you can download the WoW interface information (lua/xml) at the appropriate zip file links below: