You may have noticed that every time a new FTDI-based board is plugged in, you get a new COM port. You might also get new COM port assignment with adapters, etc. Eventually you can get into pretty high COM port numbers and that can be really annoying! For example, on my 6-month old Windows 7 install I'm already up to COM38!
First up, you'll have to open up a Command Prompt and in Windows 7 it has to be run as administrator. Open up the start menu and start typing in "Command" until the black C:\ icon appears. Right click and select Run as Administrator If you have some other version of Windows, you may not have to run as admin.