How to change the Promary ADFS federation server when using ADFS configured to used Windows Internal Database to store the configuration:
On the server you want configure as the new Primary: Set-AdfsSyncProperties -Role PrimaryComputer
On the old primary (now secondary)
Set-AdfsSyncProperties -Role SecondaryComputer -PrimaryComputerName FQDN.Primaryservername.here
To see the status of the ADFS server (Primary/Secondary): Get-AdfsSyncProperties
The primary server will indicate: Primary. The seondary will have some more information
LastSyncFromPrimaryComputerName : Primaryservername
LastSyncStatus : 0
LastSyncTime : 2016-04-11 11:42:05 AM
PollDuration : 300
PrimaryComputerName : FQDN.Primaryservername.here
PrimaryComputerPort : 80
Role : SecondaryComputer