John,
You will need to put the SD card into a PC with a SD card reader. Then go to www.naviextras.com , create a login and download the "ToolBox" onto your PC. From there, you should be able to open it up and it will auto-recognize the SD card as a 700 or 720. It will then tell you of any updates that are available. It's not very difficult, however it is not a simple as updating the Aviation Data. Thankfully, its only update every 6 months to a year, depending on the number of changes.
They have changed this site a few times so there may be a few minor changes. Once you get the ToolBox on your PC, it's pretty simple from there. The ToolBox occasionally updates as well, but that is prompted once you open it. I hope this helps.