Android 5: Change USB mode (MTP, PTP)

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[PROBLEM]
I never find where to change the USB data mode on Android Lollypop (5.0.1, Samsung Galaxy S4):
There are no "menu dots" in my storage menu.

[SOLUTION]
I still haven't found a proper way
But when I connect it to my computer, sometimes (!) it shows a notification that allows me to choose between MTP and PTP mode:

Connected as a media device
Touch for other USB options

Hmpf.