How do you update firmware on XA-NV300T?

ElDiablo12 Registered Users Posts: 14
Master Traveler
I've got this add on, XA-NV300T, can someone tell me how to update the firmware on it? Which software does it use? Neither Tomtom home or connect recognise the device. I have taken the SD card out of it, plugged it into PC and the PC recognises it as "TOMTOM G:" and I can view the files on it, but still the software says no device connected, it is plugged directly into PC, not through a hub.
How do you actually update this device?