1. Back up your "Interface" and "WTF" folders and store them away safely, then delete them from your WoW folder.
2. Extract the "Interface" and "WTF" folders contained in the .rar into your WoW directory.
3. Open up the new WTF folder, and then the Account folder located in it.
4. Rename the folder called "YOURACCOUNTNAME" to your account name. Keep caps.
5. Open the folder, and rename the folder "YourRealmName" in it to the name of the realm your character is located on.
6. Open that folder and rename the folder located in it called "YourCharName" to your character's name.
7. When you start the game, make sure to enable out of date addons.