Upgade from SQL Server 2012 cluster Evaluation to enterprise
Supported Upgrade Path for SQL 2012 can be found here:

https://technet.microsoft.com/en-us/library/ms143393%28v=sql.110%29.aspx?f=255&amp;MSPPError=-2147217396

Upgrade from SQL Server 2005 Evaluation, SQL Server 2008 Evaluation, and SQL Server 2008 R2 Evaluation to SQL Server 2012 is not supported.

So if you are just making a 2012 eval edition to a full enterprise edition it'll work.  You can do so by starting setup.exe to bring up the installation menu. 
Go to maintenance, then 'edition upgrade'
See the pic:



Or you could run the command line to install SQL Server but pass in the Product ID, using your own path, /q command optional.

setup.exe /q /ACTION=editionupgrade /InstanceName=MSSQLSERVER /PID=&lt;appropriatePid&gt; /SkipRules= Engine_SqlEngineHealthCheck