Change serial number of Mega 2560 on windows 7

Can anyone point me to instructions for changing the serial number of an Arduino Mega 2560 on Windows 7? I have done this for older Arduino boards with the FTDI usb chip using FTPROG, but cannot seem to find how to do this for this new Mega board. Thank you.

In windows xp the comport assignent is changed in the advanced comport settings in device manager.

Thanks for the reply. However, I am not trying to change the com port number, but rather the serial number of the mega board itself. On the old duemilanove boards, which had an ftdi chip, I was able to use a utility provided by ftdi called ftprog to change the serial number. I think the Mega 2560 board uses a ATmega8U2 chip in place of the ftdi chip. Does anyone know how I can change the serial number of this chip?

I did find this, but it appears to only be for Mac OS: