To change the com port (in Windows XP):
- Click on the Start menu
- Right click on My Computer
- Select Manage
- Select Device Manager from the list on the left.
You will now have Device Manager showing in the right hand pane.
- Expand the group Ports (COM & LPT)
- Double click on your device from the list (it will probably say USB Serial Port (COM20) or similar)
- Select the Port Settings tab
- Click on Advanced
You now have the Advanced Settings window showing. Here you can change the port number - for best results, select a number between 5 and 16.
If all these port numbers appear to be taken, you can select one anyway (often they are marked as still being in use when they are no longer used).
Changing the COM port for a USB device