Once you are logged into the community, you can click the "My Home" link in the left nav... Then on the next page (the "My Home" page),click the link that says, "edit profile photo."
After you click that link you'll land on the "Add Photo" page, where you need to browse for a photo on your hard drive and upload it. On thispage, be sure to select the radio button that says, "This image is: My profile photo."
That should do it! Feel free to send me a direct message if you need more help.