I'm trying to in-place upgrade my Windows Server 2008 SP1 (64bit) to 2008 R2.
Is this supported? Where can I find more information on this process?
This is a supported upgrade path.
If you did a web search for "Upgrade to 2008 R2", you would inevitably have seen this link which has all of the considerations and known-issues with in-place upgrading to 2008 R2.