The update will be live by 10 AM PDT / 5 PM GMT, if the update doesn't land in your console on listed time then you need not to worry, your console will soon be rolling out with the update. To manually check if the update is available for you or not just double tap the Xbox logo button on your controller or if you are using Kinect (a motion sensing input device) then just say "Xbox, go to settings" then head to All Settings, select system from there and then select Console Info & Updates. That'll tell you if the update is available for your console or not.
Here's the full changelog for the Summer Update:
How many of you have already receive the update? If yes, which is the feature that you liked the most in this summer update. Do let us know via comments below!