Delete server from server failed

Meet strange issue meet since I want to update my merged server verison.

Have 1 server was windows 7 which can't meet the new verison requirement.

So, I want to delete this server from merged server but it still holding online after the server was shut down. 

And I try to detech from the system, which server was defaulted and avaible to setup as new system.

But it still holding in the merged server, how can I deleted this online server.