Please make sure you removed the USB storage device from your uTrack24 front panel USB connector.
Turn off the uTrack24.
Connect the USB cable from the uTrack24 back panel to your MAC.
If it is possible please remove any other USB device from your MAC, than do a reboot.
Start the USB firmware updater on your MAC, click on the start button.
Power on the uTrack24, now it should connect, then the firmware update should start automatically.