1. Insert the dcard into a reader on your computer
2. You'll need to know the driveletter it gets assigned. We'll use E: for this guide
3. Click on START
4. Click on RUN
5. Type:
cmd.exe
6. Click OK or press Enter
7. In the black window type FORMAT E: /FS:FAT16 (it could be /fs:fat depends on which version windows you have)
That should do it. If you want to go back to FAT32 use "FAT32" as the option. NTFS use NTFS