I can only select one COM port, and it seems to be fixed for the Arduino UNO board connected.
For the early Arduino UNO's this was COM4, as also set in the preference.txt file.
For newly buyed Arduino's the possible choices are COM5 (for Arduino UNO) and COM7 (for Arduino MEGA), but the IDE sticks to communication through COM4, and so upload fails.
Please help to set the correct COM port as to be used by the IDE to upload to any Arduino.