Without even trying to research anything, I'm pretty sure there isn't a way to change the file system on a drive without formatting it (and therefore erasing your data). If you want to preserve your data, you'll need to copy all the stuff over to another location then format the target drive, and copy everything back when you're done. I can say this with the argument that file systems interpret data differently, that's why if your file system isn't supported on a system (like NTFS on Macs), you can't read the drive. I don't know how compatible the FAT32 system actually is with the NTFS system, but it's not likely that raw data from a FAT32 system would translate perfectly to NTFS. If you do manage to some how preserve your data through the conversion, you'll likely end up with lots of corrupted files.