According to www.airspaceaware.com in order to update the NATS Aware unit using a Mac, you simply overwrite the SD card with the contents of the airspace update.
More specifically, you download the latest airspace update file which will be named something like
Using the above example, we rename Airac0212.update, to Airac0212.zip, unpack it, and then copy the contents of the resulting Airac0212 directory into the root of the SD card. Simple enough, but this totally destroys any saved routes on the device.
I found that by copying the file
from the SD card to somewhere safe (shown opposite) – then performing the update as usual, and then finally copying my old Route file back onto the SD card, that any saved routes are preserved. I notified Airbox Aerospace of this, and they confirmed that “all seems to work fine with this process”.