Delete your "Interface" and "WTF" folders in your WoW directory (don't forget to backup your bindings-cache.wtf)
Extract the WinRAR archive to your WoW directory
Rename folders "ACCOUNTNAME", "Servername" and "Charactername (-Priest / -Warlock / -Warrior)"

Addon Do Not Update List:
MBB
Quartz
ItsyMM
Power Auras Classic (only referring to using the curse client)
SharedMedia and Additional Fonts (have additional textures and fonts I added, unless you know what you're doing )
Grid. If you do update, please refer to this page for the proper Lua changes you'll need to make to regain the white background.