Firstly find a picture that you want to use, it should be 100x100 in size for best results.
Once you have found a picture, go to an image hosting website, for example:
, and have the picture uploaded. Once this is done the site will supply you with several links to the picture.
Copy the link, then open up character under the manage tab and select edit character profile. You will see a character image link, replace this with the one you have collected from the image hosting website.