Open Powershell with administrative credentials:
PS C:\> $Credential = Get-Credential
PS C:\> $VMHost = Get-SCVMHost -ComputerName “<Hostname of Server here>”
PS C:\> Remove-SCVMHost -VMHost $VMHost -Credential $Credential
The Get-Credential cmd-let will open a prompt in which you have to supply credentials with the rights to remove the host. In the second line you specify the server. This doesn’t have to be the FQDN, the Netbios name will do.
The last line actually removes the server. This may take a few minutes, depending if the server responds or not. If the server does not respond, Powershell waits for a time-out.