Airties 4920 firmware update

Hi Guys,

I have couple of AT&T Airties 4920 mesh devices, however AT&T locked them from the UI, doesn't let me pass any other firmware version or change any settings.... Does any one know the serial settings needed in order to connect to this device to remove whatever is locking the firmware update ? Already tried multiple speeds, different flow controls but no luck so far.

Thanks in advance for any input.