I searched asus website for flashing instructions, but couldn't find any. I suggest you put in a technical request to asus and list your device of choice (floppy drive, usb drive, etc). The bios programs are for a usb drive. I used a floppy or a windows flash program. Get this right, or you could end up with a dead board. Check your bios version on the post screen. If your cpu works with it, I wouldn't flash it.
As o1die said, if there's nothing wrong or reason to update, don't do it.
Still, if you must, here's the page for your BIOS and Manual. Download the manual in the language you prefer and the BIOS version. The newest version looks to be 1406.
Open the manual pdf, updating the BIOS instructions start on page 54 (section 2-2). Carefully read over each method and choose the one right for you. The EZ Flash 2 Utility on page 60 (section 2-8) looks simplest.