Go to the User Control Panel : ucp.php
Click the Profile tab, select Edit Avatar.
You can then upload a picture, but the maximum dimensions are 160 x 160 pixels, so you may need to shrink or crop the image beforehand.
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"Whether I were to preach in brief, Sāriputta, or whether I were to preach in detail, Sāriputta, or whether I were to preach both in brief or in detail, Sāriputta, rare are those who understand." (A I 333, Sāriputtasutta)