The update build number JOP40C is rolling out now and should reach your devices shortly. Google has also posted the factory image for the Android 4.2 version for yakju variant on its dev site.
You can also manually download the update using this link and push it via ADB sideload. Several tutorials are available over at XDA to help you with this.
To remind you, Android 4.2 brings host of new features to your Galaxy Nexus including lock-screen widgets, quick toggles, improved performance, photo sphere and more.