Ok cmaglie,
I happen to have an Arduino Uno. The tutorial at http://arduino.cc/en/Tutorial/ArduinoISP does not mention how to update the Due firmware from an Arduino Uno. And I do not want to connect it as shown in the tutorial because of the 5V intolerant inputs of the Due. Can you describe how to connect these two boards?
Sorry, I am more on the programming side and not so much on the hardware side (that's why I opted for the Arduino).
Thanks,
Stephan