I use constraing layout in my app.
However the layout editor pops me a warning that I use the obsolete library:
Using version 1.0.0-alpha9 of the constraint library, which is
Usually Android Studio warns you about new updates by highlighting the line, then if you click on that line and press alt + enter it will popup an option to update.
Or, you can look at this instruction (the item #3), so you can see the latest version in your Android Studio SDK Manager Tools.
Or, you can also stay tunned about ConstraintLayout new updates in this link: http://tools.android.com/recent