Hello,
You can convert Windows Server 2019 Essentials (retail) to Windows Server 2019 Standard (retail), you will need to purchase a Windows Server 2019 Standard license.
More information about the license conversion can be found here:
Install, upgrade, or migrate to Windows Server
It applies to Windows Server 2019 the same way.
Purchase a Windows Server Standard license
Open an administrative PowerShell command
Run the following command to verify the target edition:
dism /online /Get-TargetEditions
You should see Target Edition : ServerStandard or something similar
Run the following command to complete the upgrade:
dism /online /Set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
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