Exactly how are you attempting to change to the COM port assignments? I believe the proper way is through the RealPort Properties:
1. Expand the Multiport serial adapters category in Windows Device Manager.
2. Double-click the Etherlite (Properties).
3. Click the Advanced tab.
4. Click the Properties button.
5. Select the first Serial port on the left, click the Serial tab, and change the COM port number in the drop down.
Does this information help?