I purchased a Windows Server 2012 Standard volume license so we could migrate to Exchange 2013. Then plans changed and we are going to install server 2008R2 and Exchange 2010. I was told that I can down grade to 2008R2 using my 2012 license then when I want to go to Exchange 2013 I can upgrade the OS to 2012 and lose no information. Do I have to install 2008 R2 standard or can I install enterprise? I am not sure I understand how to downgrade to 2008 R2 using 2012.