How to change the COM port for a USB Serial adapter on Windows 7

Start by going to the Device Manager. Once there do the following:
Expand the Ports ‘(COM& LPT)’
As you can see Windows has set the port to COM10 (xx) in brackets at the end. However many legacy applications expect the port to be between 1-4. Let’s change that:
Right click on the device and click on ‘Properties’.
Click on ‘Port Settings’. Then click on ‘Advanced…’.
Once you’re in ‘Advanced Settings for COM10’ on the bottom you can see the ‘COM Port Number: COM10’. Click on that to change it to the lowest possible number (between 1-4).
Then click ‘OK’ on all open Property Windows.

-------------how to list devices that used to be connected--------------------

1. Start, All Programs, Accessories, Right-click “Command Prompt” in Accessories and choose “Run as Administrator”
2. Enter “set devmgr_show_nonpresent_devices=1″ – without the quotes obviously
3. Enter “start devmgmt.msc”
4. In the box that opens, select “Show hidden devices” in the ‘view’ menu.

Now if you expand the section on COM ports, all the COM ports that have ever
been created will be displayed, the non present ones being in grey. You can
uninstall away anything that you don’t want (right click, select uninstall).