FYI, the option to add an avatar isn't available to you until the extra options are available. You've reached the 10 post milestone, but you also must be registered on DISboards for 24 hours before the options open up.
When you've reached that time, click on your username in the upper right and then click on "Account Details" in the pull down menu. Scroll down a little and you'll see the "Avatar" section.
Thank you, PrincessShmoo. I was following those instructions, but I wasn't able to change it until this morning. I think it takes a little longer than the 24 hours, once you have 10-12 posts.