Go to Settings > Updates & Security > Windows Update


Windows Update

image: https://winblogs.azureedge.net/win/2016/08/settings-1024×700.jpg

1. In Windows Update simply click Check for Updates.


Windows Update

image: https://winblogs.azureedge.net/win/2016/08/Checkfor-updates-1024×645.png

2. The Anniversary Update will appear as, Feature update to Windows 10, version 1607. Click update and the update will begin downloading and installing.


Source: How to get the Windows 10 Anniversary Update | Windows Experience Blog