HI
1) First type show usb device to check the usb
2) Then type copy usb://N1500v6.7.1.20.stk active to flash the firmware
3) Then type copy usb://N1500v6.7.1.20.stk backup to flash the firmware
4) After done copy the file type show version to check
5) Then type boot system back up and write to save the configuration
6) Lastly type reload to reboot the switch
7) After done reboot the switch type show version to check again