There might be a scenario where you would like to change your License of Team Foundation Server 2010 from Team Foundation Server 2010 Volume License to Trial edition for example.
A typical example would be that you want to move your existing Team Foundation Server 2010 Volume License to a high end server and would want to install Team Foundation Server 2010 Trial for your testing on the existing server.
Downgrading Team Foundation Server 2010 license is not possible. Even if you uninstall TFS 2010 Volume License edition and installs TFS 2010 Trial edition it would still work as Volume License. This is a limitation with the current License infrastructure.
The only workaround is to install a fresh OS and then install TFS 2010 Trial edition.
You can verify your current license by using the following command "TFSConfig License".
Reviewed by: Wendell Phillips & George Archer
How is it possible to change the volume license version to a retail version? Or is that also a downgrade?
Why would you like to change a Volume license to a retail License? You can change the license once you have the product Key for the product: steps are detailed at: http://msdn.microsoft.com/en-us/library/cc668758.aspx