I'm assuming that you're moving from one SD card to another that is at least as large, or larger than the existing SD card.
1) Create an image from your existing SD card using this util:
http://sourceforge.net/projects/win32diskimager/
2) Write the image you just created to the new SD card using the same Win32Diskimager
3) If the new SD card is larger than the old one, then extend the Fat32 partition using this utility:
http://www.easeus.com/partition-manager/epm-free.html
Keep the old SD card until you get the new SD card to work properly.