It's flash was added later for some strange reason, so for the earlier bios updates you need to update with the dos file, to do that, download the dos version of the bios, also download this:
https://rufus.akeo.ie
Now plug in your USB stick and open rufus, select your USB stick at the top, then partition scheme for bios and uefi, fat32 in the next box, default cluster size, label leave blank, put a tick in quick format, and create a bootable disk using freedos, and finally a tick in create extended labels, then start, only takes a min or 2 to complete.
Next extract the contents of the bios zip file to the USB stick, not in any folders or anything, just on the root of the drive.
Now reboot your computer and boot off the flash drive, you'll enter dos mode, at a C prompt, you'll have to cd to the correct drive, usually D is the USB stick, but sometimes it's A: then type the file name that's on your USB stick, probably an exe file, something like H87Pro~1.exe then press enter, leave it to do its thing. Do not remove the USB stick until you are safely back in the bios.