Cannot update bricked GL-A1300 with UBoot

I download the latest stable file (openwrt-a1300-4.2.1-0414-1681478660.img) for Uboot to my MacBook Pro but it thinks the file is an unreadable disk. What gives?

Are you using the USB to Uboot?
Is this saved to a USB on your computer and because its a .img file it wants to boot from it

No. I downloaded .img file directly to my computer so there is no external device being used. It looks like any other file package installer but is not acting that way.

If you saved it on the desktop I think apple tries to auto start and it thinks its a drive is my only guess cause its a .img file.