I have several domain controllers running Windows Server 2012 with a domain and forest functional levels at Windows Server 2012. Two of the DCs are running ADFS (2.1) in a farm for users in my organization to authenticate to Office 365. I'm in the process of replacing my domain controllers with Windows Server 2012 R2; however, I haven't been able to find a "best practice" method of upgrading ADFS. The only process I've seen posted online basically tears down ADFS and sets it back up from scratch, but I'd like to avoid that if possible to minimize down time for users.
The migration guide suggests exporting the current config and importing it to a parallel install. You can then point users at it. Therefore, downtime is negligible. There is no tearing down involved.