In Windows, Windows Registry works as a configuration settings database for installed apps, Windows services, etc. Windows Registry is the best way to change the default RDP port from 3389 to the desired custom port. Here you go with a complete step-by-step guide to change default RDP port.

Step 1: First, right-click on the start menu and click on the Run option, or you can use the Windows+R keys on the keyboard to open the Run utility. Then, type the regedit and press OK to launch Windows Registry Editor.

regedit 

Step 2: In the Windows Registry Editor, go to the below path and click on the following registry folder:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp

Step 3: After that, double-click on the PortNumber in the RDP-TCP folder.

Step 4: Select the Decimal option in the Edit DWORD(32-bit) value box and type a new port number. You can select the values between 1 and 65353.

Important Note: You have to ensure that the values don’t match any common ports, so if you select a common port (like port 80 for the web traffic), you can’t establish the Remote Desktop connection afterward. 

Step 5: Finally, press OK to save the changes and restart the system to make changes successfully.