How to Reformat a Flash Drive With a Macby Regina EdwardsUpdated September 28, 2017
USB flash drives, or thumb drives, are convenient tools to transport and transfer files between computers. Currently, PC and Mac files can access files on USB flash drives by reading the drive as a peripheral. Mac users can easily reformat USB drives using the Disk Utility application included in OS X to optimize the disk space for files.
Locate and launch the Disk Utility program in the Utilities folder located in the Applications folder. Insert the USB flash drive in the appropriate slot in your computer.
Click the USB drive (usually named "Untitled" if it is new) in the left hand frame.
Click the "Erase" tab in the main frame (right hand side). Select "Mac OS Extended (Journaled)" option in the drop-down menu under "Volume Format." Type the name of your drive under "Name."
Click the "Erase" button. Click the "OK" button in the dialog box to confirm you want to erase all files.
Exit the Disk Utility application (select "Quit Disk Utility" under "Disk Utility" in the top menu bar). Open a new Finder window and verify that you see your USB drive in the left hand side of the window. Unmount your USB drive by selecting the drive and clicking the triangle to the right of the icon (or click "Eject" under "File" in the Finder's top menu bar).
If the USB drive contains read-only files, select the drive and click "Get Info" under "File" in the Finder's top menu bar. Click the box next to "Ignore ownership on this volume" in the "Ownership & Permissions" section. Then launch Disk Utility to proceed with formatting.