Should you happen to be part of the Windows Phone Preview for Developers program, this is what you are required to do. Firstly, go to Settings > Phone Update > Check for Update and see whether you are able to obtain the update from the server. The Preview for Developers program would then provide members with the ability to view Windows Phone OS updates prior to their release to the masses. Developers will then have the upper hand as they can ensure that all of their apps would run smoothly on a new build of Windows Phone.
Microsoft claims that this new update will contain “our usual scope of fixes and improvements. We’re requiring this update so we can continue to test our update systems. The update will show as a “critical update” on your phone.”