I know that a true upgrade (such as Win2k8 to Win2012) of the operating system isn't supported. Here's the page that says the above statements: https://technet.microsoft.com/en-us/library/bb691354%28v=exchg.150%29.aspx
Specifically, there's the following: "You can't upgrade Windows when Exchange is installed on the server."
I believe the same is true for changing the operating system from standard to enterprise, and I haven't been able to find anything in searches that states otherwise.
Hi,
As what Will says, we can't upgrade Windows with Exhange server installed. If you want to upgrade the Windows server version for Exchange server, please install a new server for Exchange server.
Regards,