Microsoft: Upgrade Options for Windows Server 2012 R2

The table below briefly summarizes which already licensed (that is, not evaluation) Windows operating systems can be upgraded to which editions of Windows Server 2012 R2.

Note the following general guidelines for supported paths:

• In-place upgrades from 32-bit to 64-bit architectures are not supported. All editions of Windows Server 2012 R2 are 64-bit only.
• In-place upgrades from one language to another are not supported.
• In-place upgrades from one build type (fre to chk, for example) are not supported.
• If the server is a domain controller, see http://technet.microsoft.com/library/hh994618.aspx for important information.
• Upgrades from pre-release versions of Windows Server 2012 R2 are not supported. Perform a clean installation to Windows Server 2012 R2.
• Upgrades that switch from a Server Core installation to the Server with a GUI mode of Windows Server 2012 R2 in one step (and vice versa) are not supported. However, after upgrade is complete, Windows Server 2012 R2 allows you to switch freely between Server Core and Server with a GUI modes. For more information about these installation options, how to convert between them, and how to use the new Minimal Server Interface and Features on Demand, see http://technet.microsoft.com/en-us/library/hh831786.

If you do not see your current version in the left column, upgrading to this release of Windows Server 2012 R2 is not supported.

If you see more than one edition in the right column, upgrade to either edition from the same starting version is supported.

Reference:
1.  Upgrade Options for Windows Server 2012 R2
http://technet.microsoft.com/en-us/library/dn303416.aspx