1. Take the first SD Card out of the 3DS.
2. Put the SD Card into your MAC or PC(Windows XD). Or if they don't have an SD Card slot, put the SD Card into an SD Card reader, and put the reader into the USB outlet.
3. Select ''Open Folder to view Files''.
4. Highlight the SD Card Data and paste it to the 3DS Data File.
5. Eject the SD Card and put the new SD Card in.
6. After you do step 5, go to the My Computer window, and make the SD (E:) format FAT32.
7. Click on the ''Open Folder to view Files'' option again.
8. Copy the data on the 3DS Data File and paste it to the new SD Card's Folder.
Note: If you don't have a 3DS Data File, you can create one. This has been tested, and results may never be vary.
To show you it's true, here is a video to show you it's true.