In windows, it is listed in the "device manager".
Or you can connect the board to the arduinoIDE and see the list of available com ports.
One is named
COM XX (arduinoMega or Mega2560)
If you have more than one Mega board, the assigned com ports are different, too. You better put a sticker on the board and write the com port down. ( I´m in the COM 50+ region already...)
-Olaf
Edited 3 time(s). Last edit at 07/13/2015 01:57AM by o_lampe.