1) Insert a USB flash drive into your Mac.
2) Press Command ⌘ + Spacebar and then search for Disk Utility.
3) Select the USB flash drive you wish to format. i.e. RED USB
4) Select the Erase button and set Format: MS-DOS (FAT) and then Erase…
5) Copy the upgrade file(s) to the formatted USB Flash drive.
6) Eject the USB flash drive by clicking on the Eject icon next to the name of the device in the Finder window. You can now safely remove the USB flash drive.