Ok this is actually easy to solve and wont require you to redownload the whole game.
Step 1) go to the world of tanks website (download section) and check the version thats out right now. There will be a thing that says upgrade from #### to####. Remember only the "from" part
step 2) open your world of tanks folder in either games or program files
step 3) open the file "version".xml in notepad
step 4) change the version variable to the version before the update
step 5) launch wot
step 6) it will patch itself
step 7) enjoy