1. Open hard disk utility!
2. For Mac OS High Sierra: Under "Appearance" - "Show All Devices", so that the physical drives are also displayed in the sidebar.
3. Select the parent drive (for example, "General USB Flash Drive" or "SMI USB DISK Media")
4. Select "General USB Flash Drive"
5. Click "Delete"
6. Optional: Enter the name under "Name"
7. Select "MS-DOS file system (FAT)" format
8. Select Master Boot Record Scheme
9. Click "Delete" (Attention! All files on the selected drive will be deleted.)