There are two item that should be modified to change the default 3389 port:
One is: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\rdpwd\Tds\tcp]. Modify the PortNamber to the one you want.
The other is: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentContro1Set\Control\Tenninal Server\WinStations\RDP\Tcp]. Modify the PortNumber to the one you want.