Downgrade Domain and Forest Functional Levels in AD

Starting with Windows Server 2008 R2, you can roll back the forest level and the domain level after you have raised them.

• The minimum target DFL that you can downgrade to is Windows Server 2008.
• You can’t roll back to the Windows Server 2008 functional level after enabling the AD Recycle Bin. You can check if the AD Recycle Bin is enabled in your domain:

You can only downgrade using PowerShell (you can’t do it using the GUI).

Open a PowerShell console with Domain Admin/Enterprise Admin privileges. Check the current FFL: