I'm assuming you have a PEz? You are correct that you want to use the most recent firmware. You may notice that it's from December, so there's no way it could be installed on your reader at the factory. There's a video on YouTube where Amy shows how to upgrade the firmware. I think the volume button is for the 6". On my PEz, I push the page forward button on the left side. Watch the video to see which button I mean.
http://www.youtube.com/watch?v=8USEOxj8P2M
One other note. Make sure that you've fully charged your reader before you start. We're told that running out of power in the middle of the upgrade is really bad.