Upgrading brocade firmware from USB is really simple.
Just follow this procedure.
Keep in mind that Brocade switches support firmware download from a Brocade-branded USB device. You cannot use a third-party USB device.
Upload and apply firmware
firmwaredownload -U /usb/usbstorage/brocade/firmware/v7.3.0
Disable USB (You must unmount the USB device)