обновить релиз серверов Windows (Standart -> Enterprise или на Datacenter) можно без переустановки системы.

Windows Server 2008 R2/2012 contains a command-line utility called
DISM (Deployment Image Servicing and Management tool). This tool has
many features, but one of those features is the ability to upgrade the
edition of Windows in use. Note that this process is for upgrades only
and is irreversible. You cannot set a Windows image to a lower
edition. The lowest edition will not appear when you run the
/Get-TargetEditions option.

If the server is running an evaluation version of Windows Server 2012
Standard or Windows Server 2012 Datacenter, you can convert it to a
retail version as follows:

If the server is a domain controller, you cannot convert it to a
retail version. In this case, install an additional domain controller
on a server that runs a retail version and remove AD DS from the
domain controller that runs on the evaluation version.

From an elevated command prompt, determine the current edition name
with the command DISM / online /Get-CurrentEdition. Make note of the
edition ID, an abbreviated form of the edition name.
Then run

providing the
edition ID and a retail product key. The server will restart twice.