During installation, some settings from the existing instance of Windows Server Update Services (WSUS) will not be preserved. ...

During installation, some settings from the existing instance of Windows Server Update Services (WSUS) will not be preserved. If the existing server is a downstream server (DSS) it will be configured as a standalone server when the upgrade process is complete.  If the existing server is an upstream server (USS) you will need to configure all of its downstream servers to use either a different USS or Microsoft Update.  We recommend that you reconfigure your downstream servers before proceeding with this installation.