Renumber the COM port of those devices on the device manager.
Or delete the device instances of the VCP.

I recommend you to renumber them.
Some devices like SiLabs have two device instances for single VCP port.
- One under Port(COM and LPT)
- One under USB controller
When just the 'Port' instance is deleted, the other one disappears from the device manager screen at the same time. But it doesn't mean the instance is deleted completely. On SiLabs case, the 'USB controller' instance have to be deleted first.

To renumber the COM port number,
1) Copy these two lines to a blank text file, and rename the file to DevManager.bat

set devmgr_show_nonpresent_devices=1
start devmgmt.msc

2) Double click DevManager.bat, and Device Manager comes up.
From 'View' menu, select 'Show hidden devices'
Then you can see all devices, even if they are not connecting now.

3) Expand Port(COM and LPT) and find the device instances.
Double click the instance, and select port tab.
Push advanced button.
You'll see COM port number pull-down at the bottom of the dialog.

Tsuneo