I've upgraded software in two of my HB units so far and downloaded the upgrade software version to my computer and used Humminbird PC application..free download from HB site...to download to the unit. You do need the cable however, so the memory card is prolly an easier way to do it. There is a way called "bootstrap" to get out of trouble if things go wrong. That is also explained on the HB site. You really do want to join the HB SI forum site like Kosmo suggested. I did have to use this method once, but the other times the upgrade went smooth. Good luck.