in the page: arduino.cc/en/Guide/Windows#toc4 two things:
- Right click on the “Arduino UNO
(COmxx)” port and choose the “Update Driver Software” option. Change to: COMxx.
- Finally, navigate to and select the Uno’s driver file, named
"ArduinoUNO.inf", located in the “Drivers” folder of the Arduino Software download. Change to: “Arduino UNO.inf” (with space)
- And then fall a next point: displays a warning. Say “OK”.