(1) Click on the Windows Start icon in the bottom left of the desktop
(2) In the [Search programs and files] area, type
…but don’t press Enter.
(3) Right click on the cmd icon that appears at the top of the list dynamically generated above it and select
Run as administrator
(4) Congratulations, you now have command line with administrator privileges. Now, type the following two commands to launch Windows Device Manager in a way that allows you to view unused ports (note that some websites misspell the name of the environment variable in the first line as “devmgr_show_nonpresent_devices”, which doesn’t work, *sigh*):
set devmgr_show_nonpresent_devices=1 devmgmt.msc
(5) Congratulations, you are now running Device Manager with secret settings. From the menu bar, enable the following entry (and make sure it ends up ticked):
View -> Show hidden devices
(6) Now you should be able to click on the Ports (COM & LPT) icon to have a look at all your COM ports, both used and currently unused. Right click on the particular unused one you want to remove (I had 40 of these before I found out this trick), and from the context menu select:
(7) Confirm that you genuinely want to uninstall it: and there you go.