From your profile, select "edit my preferences" from the links in the "community" box above your username. This will take you to a screen with several options for editing your profile. On the right, in the middle box, is an area to either select an icon or to upload your own photo. Your icon will be visible automatically. If you choose to upload a photo, it must go through moderation first. Also, if you upload your own photo, try cropping it into a square first so that it does get stretched or distorted in the circle.