Windows 10 download site to get the latest release. This installation is driven by the upgrade assistant where you can create media or perform the in-place upgrade to Windows 10 1703.
For enterprise customers and developers, the ISO media for Windows 10 1703 can be found on your volume licensing site or MSDN. If you are building Windows images for deployment be sure to update your ADK environment to 1703 as well hosted over in the hardware developer center. There has been some news about potential issues with the new ADK so review the following blog articles by MVP Mikael Nystrom:
OS Deployment – Installing ADK 1703 on Windows Server 2016 could fail
OSD – App-V tools are missing in ADK 1703 when being installed on Windows Server 2016 (sometimes)
Need to know what is new with 1607 for IT Pros?
No problem, Microsoft has published documentation over here.