How to upgrade to macOS Server from server running OS X 10.9.5 and OS X Server 3.2.2 How do I upgrade to macOS Server from a server running OS X 10.9.5 and OS X Server 3.2.2? I would assume that I simply upgrade the OS X to macOS, then buy/download/install the macOS Server app from App Store. Of course, I will have a full backup of server before taking these steps.

Currently, we are only using the server for File Sharing and Time Machine. Am I missing any other steps? After upgrading, should my existing file shares and Time Machine backup still be configured as before? 

I tried to upgrade to macOS Sierra and got this message:


  macOS Sierra supports macOS Server version 5.2. To upgrade your Server
  data you will first need to install OS X 10.10 or 10.11 and OS X
  Server version 4 or 5. Installing macOS Sierra on this volume will
  disable the current server functionality. Are you sure you want to
  continue the installation?


I am unable to find OS X 10.10 or 10.11 in the App Store. If I continue installation, and then upgrade to macOS Server, will I have to reconfigure my server or will it be upgraded?
I successfully could upgrade server 3.2.2 (osx10.9.5) to macos server 5.2 (sierra) on my mac mini by following steps.


Install Yosemite to your mac.
Purchase Server 5.2 with your Apple ID. You can buy it on the mac 10.11.6 or later.
Open App Store. Select Server 5.2 and Press INSTALL button. The operation leads to install Server 5.0.15 !!!
Launching Server 5.0.15 will proceed the migration process.
And then install Sierra and Server5.2.


More info in my weblog below (in Japanese...)
http://memorandums.hatenablog.com/entry/2016/10/26/220901