How to Force an Android Device to Find a System Update
Whenever Google releases a new version of Android for its Nexus devices, it doesn’t roll out to everyone at once. It may take several days before your device receives the update, but you don’t have to wait.
Note that this only works if an OTA (over-the-air) update is actually available – for example, if you’ve got a Nexus 4 running Android 4.2.1 and you haven’t yet received a notification to update to Android 4.2.2. This won’t help if you’re using an Android device that isn’t receiving updates.