How to delete music video files

[aammat]

I just got my J3 (16gb) and by mistake I transfered music video files from my pc (using the USB cabel) that the J3 didn't support.. But when I connect the J3 to the PC by the USB cabel it only display the supported files and therefore I can't deleted the unsupported files that way.. I have set the USB mode into MTP, but that didn't help..
When I try to do it through the J3 browser mode I get the menu bar at the bottom, but the "X" isn't illuminated/active and I can't delete the files that way either..

Is there anoher way to do it..?

Firmware 2.26 is installed..

[aammat]

The problem is solved, I think..!

The delete function works when browsing folders and not when browsing artists or albums..