When you change network settings in a Windows virtual machine, you must reset the network stack of the virtual NIC to adopt the new settings. For a Windows guest operating system, you must disable and re-enable the network connection so it adopts a new MAC address. To perform this task with PowerShell, use the Restart-NetAdapter cmdlet.
The cmdlet is described in more detail at https://technet.microsoft.com/en-us/itpro/powershell/windows/netadapter/restart-netadapter.