Microsoft have released a new preview build of Windows Server for Windows Insiders. The new release supports in place upgrades from version 1709 so you can take you 1709 build to the latest insider builds. The download is available in ISO ad VHDX formats and don’t require a product key.
What’s New in Build 17079 for Windows Server
In-place OS Upgrade: Customers are now able to upgrade their Windows Server, version 1709 installations to the current preview build using In-place OS Upgrade. This feature is available starting in build 17079. This feature also enables customers to perform build-to-build upgrade of the next released preview build.
Running setup.exe, customers should be presented with the option to “Keep personal files and apps”, which causes the migration steps in setup.exe to run and upgrade Windows Server while preserving applications, data, and user settings.
Head over to the Windows Insider Server page for the download.