Yeah, then just insert the USB drive, open windows explorer, right click on the USB drive letter/name and select "format" (make SURE you selected the USB, it will erase whatever drive you've selected) then make sure "FAT32" is the selected option then hit "START". Once that's done, copy the update files over to the USB in the root (main) directory. When it's finished, right click on the USB letter/name again and select "EJECT." When it tells you it's all clear, remove the USB, insert it in the powered off pinball machine then turn it on.
If it doesn't go into upgrade mode at that point, power off and try the other USB port on the CPU board. Power on. If THAT doesn't work, you have a USB brand/model Spike doesn't like. Get a different one and try again.