Upload the picture you want to a image hosting web site, i use photobucket. Get the link to the image, it gives you it below the image on photobucket, or right click the picture and select properties and it is the address (URL) Log into this website. Go to profile at the top Scroll right down to the bottom to avatar. Insert the link to the image where it asks for "Link to off-site Avatar:" Click submit.
If all else fails then attach a pic to an email and send to me with a note of your username and I'll add it for you. steve@cancuncare.com