You re-set it by pushing the little button on the bottom of the unit. You have to look REALLY closely to see it, it's on the bottom where the serial number is, and it isn't actually a button, it is just a small circle on the bottom with reset written under it in tiny writing!! you re0set it by pushing it with a pen or similar.
The factory re-set will just put everything, function wise, back to original (volume,voice,map etc etc)
