Hi there
I downlaoded 2.4 today but it was hard work, had lots of problems with the updater coming up with messages syaing that something was wrong, can't remember what but here we go.
1. Go into your data folder and delete patch.mpq and patch-2.mpq(didn't have this but if you do delete it.)
2. Now click the repair tool and it will say WoW is seriously damaged and needs to be de-graded. Click Check and Replace files(not sure if that's it.)
3. Now blizzard will say download 2.4.0 Downloader, don't do this, it takes to long for people on slower internet conections so now here comes my way. Click on 2.3.0 Downloader and set that running, because you've run it before it'll run through really quickly, then update quicky. After every patch it will automatically open WoW Launcher and start downloading the next patch. Do this untill it has downloaded all the patches, hopefully you won't get an error when you do 2.3.3 to 2.4.0.
Hope this helps,
Swordfish999