I have a Lowrance 5200c and I read the instructions on doing what you need. I bought my Sd card from Staples...The very best one they had was $ 24.00 on sale and I used 3 empty print cartridges from my PC to get an additional $ 9.00 off the cost of the SD card...So I bought my 2.0 gb Sd card for $ 15.00....

If you have a slot for the SD card on the front of your PC, then slide in the SD card and then go to the Lowrance Web site and get the newest update for your GPS unit... But first make sure you know what version you already have on your unit... After verifying the version you have...Download the nesest one you need and then take out the SD card. Go install the card and then hit menu and go down to load /save info...Select load and instal the newest version into your unit..... Good Luck...