No Option to Update BIOS

My XPS 2720 AIO has a very old version of the BIOS (A02). I followed the instructions on the Dell site to create a BIOS update USB drive. I formatted the drive to FAT32, and downloaded the latest. When I hit F12 to enter the boot options, there is no option for "Update BIOS From Flash". How can I update the BIOS? I also can't boot into the hard drive (which is why I am trying to update the BIOS).