Hello,
What edition of Windows server 2016(standard...) ? And What edition of Server 2019 you want to upgrade to?
Ensure that your hardware meets the system requirements for Windows Server 2019. Make sure your server has sufficient free disk space, memory, and meets other hardware requirements.
Hardware requirements for Windows Server, please refer to this link : https://learn.microsoft.com/en-us/windows-server/get-started/hardware-requirements
Best Regards