How to use an older patch for World of Warcraft?

How do I get rid of a patch (for example 3.0.1) and use an older one (for example 2.4.3)? I need to know this because for some reason World of Warcraft: Wrath of the Lich King has installed onto my computer and I want to get rid of it so I can get it when it comes out and when I have a level 55.