Questions needs to asked before we need upgrade TFS 2013 upgrade to TFS 2018 upgrade? : One of our client wants to move from TFS 2013 to TFS 2018. We don't have much information about the current TFS setup at client's end. 

Can anyone please guide with what questions we need to ask to client to get the information regarding the current TFS setup system before we start with upgrade process.

Also share if there is any process document regarding upgrading the TFS 2013 to TFS 2018.
 
Thanks in advance.

Regards,
Pravin Kumbhar