Things to consider, when upgrading the Microsoft server license discussed here, We had a fully working Server 2019 Essentials Server. The problem was we exhausted our user Cals. So we purchased Server 2019 Standard and Client access licenses.
Server preparation was make sure there were no current windows updates. Ran check disk then shutdown the server and then restarted.
This process can take up to 30 minutes to upgrade and then server reconfiguration.

Let’s walk through the upgrade process.

Purchase a Windows Server Standard license

  1. Open an administrative PowerShell command
  2. Run the following command to verify the target edition:
    dism /online /Get-TargetEditions
    You should see Target Edition : ServerStandard or something similar
  3. Run the following command to complete the upgrade:
    dism /online /Set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
    Change the edition and product key to match the ones you have.

Output from PowerShell

Windows PowerShell
Copyright (C) Microsoft Corporation. All rights reserved.
PS C:\Windows\system32> dism /online /Get-CurrentEdition
Deployment Image Servicing and Management tool
Version: 10.0.17763.1518
Image Version: 10.0.17763.1577
Current edition is:
Current Edition : ServerSolution
The operation completed successfully.
PS C:\Windows\system32> DISM /Online /Get-TargetEditions
Deployment Image Servicing and Management tool
Version: 10.0.17763.1518
Image Version: 10.0.17763.1577
Editions that can be upgraded to:
Target Edition : ServerStandard
The operation completed successfully.
PS C:\Windows\system32> dism /online /Set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
Deployment Image Servicing and Management tool
Version: 10.0.17763.1518
Image Version: 10.0.17763.1577
Starting to update components…
Starting to install product key…
Finished installing product key.
Removing package Microsoft-Windows-ServerSolutionEdition~31bf3856ad364e35~amd64~~10.0.17763.1
[==========================100.0%==========================]
Finished updating components.
Starting to apply edition-specific settings…
Finished applying edition-specific settings.
The operation completed successfully.
Restart Windows to complete this operation.
Do you want to restart the computer now? (Y/N)

Jarvietech