You do not need to do this you don't want to. There is a risk that you will brick your microserver. Do so at your own risk.
The main reason I see for updating is to enable hot swappable drives (which means you can plug in drives while the server is on)
What You Need:
USB drive that will be formated (it will lose all its data)
No point re-inventing the wheel, there is a good guide for this here. Skip to the "Step-By-Step Guide – Critical Path Check List" section, but instead of using the files they link to, use the ones above to get the latest BIOS.
When you have succesfully installed the BIOS, restart the microserver and press F10 to enter the BIOS. Follow the steps on the previous link labeled: "Modifying the BIOS"
And that should be it fully installed and ready to go!