What are the ways to update to the latest version of the program may take back to the state it was in before the update ?
If the update fails, then wyUpdate automatically rolls back to an old version. If the update is successful, then the only way the customer can install the old version is for them to use an old installer of your app.
And What again how to update to the latest version?
The same way you always update: http://wyday.com/wybuild/help/walkthrough.php