Anniversary Update is officially available via Windows Update to Windows 10 users using version 1511, while it may take more than one day for AU to show up in the Windows Update as it could be still rolling, however, you can still able to get anniversary update and install in another way on your device (this is official method of obtaining Anniversary Update, recommended by Microsoft other than Windows Update method), that’s by using Windows 10 Update Assistant.
Forcing Windows 10 to download and install Anniversary update using Windows 10 Update Assistant
To get started, visit Windows 10 update history page and click on Get the anniversary update now
Windows 10 update Assistant will be downloaded to your computer, run it and click on ‘Update Now’button to start the process. The tool first checks your PC is compatible, after that only you can begin the download.
Wait and keep your PC open while Windows 10 update is being downloaded to your computer, depending on your internet connection speed 4 GB update download may take more time.
Note: There are reports that Windows 10 Media Creation tool has been updated to give this update, while Microsoft hasn’t confirmed that, its better for you to get anniversary update using Windows 10 Update Assistant.