step 1: Open up Registry Editor by running regedit.
step 2: Then navigate to HKEY_LOCAL_MACHINE, SYSTEM >> CurrentControlSet >> Control >> Terminal Server >> WinStations and RDP-Tcp.
step 3: Right click on the PortNumber dword and select Modify. 
step 4: Change the base to Decimal and enter a new port between 1025 and 65535 that is not already in use.