There's a saying..... RTFM.
Page 57 of the manual gives you the procedure for formatting a new SD card. As for dumping the files, you might be able to just copy the files from your SD card to a folder on your computer. The DP03 stores data in two separate areas, an MTR partition where the actual audio data resides, and and FAT partition which is supposed to be where the computer will find master tracks, etc. I don't know if your Mac can access the MTR partition directly. Or you can use the procedure in the manual... pages 60-65.
Personally, I have quit deleting anything off my SD cards. It only took one time of overwriting the wrong card to learn my lesson.
Just buy a new one for $10, flip the write protect tab on the old one, and file it away for the day you want to revisit those projects. I have a box with envelopes, each marked with the contents of the SD card inside. Tape guys spend $50-100+ on a single reel of tape that might have 20 or 30 minutes of music on it. Start thinking of the cards as tape reels. Buy a 10 pack for $70 and you're set for a few years.