[briHass]

They're done over USB. The system will look for specially named firmware files (*.up) and auto-apply.

This forum: http://mazda3revolution.com/forums/2014-mazda-3-skyactiv-aud... has some excellent info, and someone usually posts the new FW files. I've done an upgrade and the hacks myself.

[mikeash]

Nice. Not quite as convenient as Tesla, but it's great that they give you the ability to do it yourself.