Determining the Serial Port COM number

Open the Control Panel from the start button on the Windows taskbar.

Double click on the System icon

Select the Hardware tab

Click the Device Manager button

Expand the section called Ports (COM & LPT)

Identify the Communication port and make a note of the port number (COM1 in this example)

If you are using a USB to Serial Adapter, the entry may be someting like:
Prolific USB-to-Serial Comm Port (COM3)

Close all of the above windows