1st step: Enable RDP in System settings. You can go there by right clicking on Computer -> Propreties. Choose Advanced System Settings from the left side menu.
2nd Step: Change RDP Port: Open the registry editor (regedit: open cmd -> regedit.exe). Select HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations\RDP-Tcp\PortNumber . Change to decimal mode, and change the port number, then click ok.
3rd Step: Enable the new Port in the Firewall settings. Open Server Manager, Select Firewall Settings in the left menu, right click on Inbound Rouls -> New. Choose TCP, set Port number, and name it.
Thats all. After this you should restart your server, then everything should work fine. Default port for RDP is 3389 (TCP). Enjoy.