It's a bit difficult to know the version because, since there's a Live Update feature and the installers also download all the latest code when they start, it's difficult to end up being outdated, at least for the program features and code.
The only thing not automatically updated are the Vehicle liveries so, depending how old your installation is, you might need to download one of 3 different vehicle updaters, which includes all vehicles released after a certain date, indicated on the download buttons.