If you need a temporary HFS+ partition to expand your files onto, you can make a Disk Image with Disk Utility. It's better to get to HFS+ and have it over with, though. I am not aware of a file system converter, so you'll have to reformat. eEst way to get your files off is likely to make a disk image large enough to hold all of them (in HFS format), copy your stuff, reformat and restore from the image.