Delete unused COM ports

1. Click Start -> Run -> type cmd
2. Type set devmgr_show_nonpresent_devices=1 then press Enter
3. Type devmgmt.msc then press Enter
4. Click View -> Show hidden devices
This will display devices that are not connected to your computer.
You can right-click, then select Uninstall to remove them.

Credit: http://www.mp3car.com/vbulletin/software-software-development/110742-delete-unused-com-ports-say-inuse.html