Go to Profile - Forum Profile Information then you should see a profile picture thing. Just click ''Browse'' or get a URL of a picture. When you have that done go down to the bottom and click ''Change Profile''
Try this if you need help with your own pictures to get URLS for them - http://feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=8658.0 (http://feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=8658.0)
Hope this helps!