Today Microsoft released the 2nd Windows Server 2016 Insider build (16257) and the Remote Administration Tools (RSAT) to manage it on Windows 10.
Unfortunately, There is no way to update an existing Installed Insider build VM using Windows update and we have to download the Image and Install it again on a new VM.
To download the new build go to the link below and download it (registration required, click here for more details)
The new build, 16257 Includes a major feature that was announced a few months ago The Windows Subsystem for Linux (WSL) which allow us to run native Linux environments on Windows Server.
Also In this build a new Windows Nano Server 2016 Container Image.
And the new RSAT tools for Windows 10