Please note that you cannot change avatars at the moment.
We are currently using something called Gravatar, which makes avatars available for those that use this free service.
We intend to let you select Gravatar or upload your own avatar in the near future. Right now, please bear with us and either use Gravatar or wait until we have the new feature ready.
If you need to refresh your avatar, head out to your preferences, edit your profile picture and hit the refresh button.