Dear Muhammad:
Thanks for contacting us. Yes the 15.1 inches display do not have the USB mini interface. So the download must go through USB disk.
To use the USB disk, you must have a blank FAT32 USB disk (the one in the accessories will be OK). First, plug it on your PC, and use the “Download to USB disk function” (it is beside the online download button). A “VT_set” folder will be downloaded to the USB disk if this step succeeds.
And then plug the USB-disk on the display, the download will auto start.
Please let me know if you have any other questions.