Open Hyper-V Manager, click Hyper-V settings.
Click Live Migrations on the left and then Enable incoming and outgoing live migrations
Here you can configure how many live migrations the server can do at the same time and the network the server should use for live migration.
With PowerShell you enable live migration :
enable-vmmigration add-vmmigrationnetwork 192.168.122.1 set-vmmigrationnetwork 192.168.122.1 192.168.122.140 set-vmhost -virtualmachinemigrationauthenticationtype kerberos