Go to your settings. Now you're under pressure to come up with something witty and funny. Or we will definitely make fun of you.
First email [email protected] and ask them. They probably won't reply. Just send them another email, and continue to do so until you get a response. Next you fill out an application for Avatar. Once this is approved by the 6pack Board of Directors, you then have 6 hours to submit your avatar graphic. Once that happens....ah 17 it.
Go to "Settings" at the top right, and click "Edit Avatar".