You have the latest version. The latest stable version. The latest version you are talking about is the beta versions which you can get on steam, you just have to activate it. As aphrodite says, you can activate the beta versions by following his link, it will show you how...
BUT, the downside with using the steam version and beta releases is that steam installs the beta steam client version too, which is prone to bugs on the steam end.
If you use steam for games, expect issues