In order to change one service port number in Windows systems, you need to change the services file in the %SYSTEMROOT%\SYSTEM32\DRIVERS\ETC folder (usually c:\windows\system32\drivers\etc).

For example, I need to change the udp port number for the SNMP service. To do this edit the file c:\windows\system32\drivers\etc\services with notepad, or any other text editor, and in the line:

snmp              161/udp                           #SNMP

change to:

snmp              port_number_you_want/udp                           #SNMP

Save the file and restart the SNMP service in the services.msc.