Thanks very much. It was so easy even I could or did do itUse the User CP (control panel) option "Edit Avatar".
You can use a photo or image you have but you will need to edit it to fit the maximum size of 155 by 160 pixels or 45.2 KB (whichever is smaller).
Use any image editing software, I like Irfanview (just google it) its free and very easy to use to resize your photo.
Please note, an avatar is visible to anyone even guests so the image cannot contain genitals or other X rated content.