Webby,
With the latest software update, you can now save that UpdatePackage.zip file right on the SD card. Then insert the SD card into the iFly 520 (even 700 and 720) and boot the unit up and select the Update Option at the start up screen.
You cannot use a cable to connect the iFly 520/700/720 directly to a computer. It's not the same usb port as most other units since we use this USB port to drive out Serial and NMEA data for autopilots, etc. I hope this helps.