A. Changing the port that a service uses depends heavily on the service. For example, you can set HTTP's port with the Internet Service Manager (ISM).
As a general rule, you can change the port by changing the %systemroot%\system32\drivers\etc\services file with a text editor (e.g., Notepad). For example, to change the port SNMP uses, open the file and modify the following lines:
snmp 161/udp #SNMP snmptrap 162/udp snmp-trap #SNMP trap
Change 161 and 162 to the ports you want to use, and save the file. You must restart the computer for the change to take effect.