I have the same Mobo and I updated my Bios when I upgraded to a phenom 2. I believe I used a utility that I downloaded from the Asus site. I had a number of of Bios versions to upgrade through to get to the one I have installed. To be honest I even got an error message during the process but I was still able to upgrade to the Beta version that I needed.
Anyhow like henydiah says I would only upgrade your Bios for a specific reason (in my case to support the CPU I wanted to add). I would be very surprised that a different graphics card is a reason to upgrade your bios.
just FYI..I am running the M2N-SLI deluxe on the Beta Bios (version 5001) without issues for at least 6 months. I did it to get Phenom 2 support. I think it eliminates the ability for a LAN hardrive. I have not had any issues as I am using a normal HD through SATA.