As fatweed said--it is under the Avatar control panel and you upload it from your computer. It can be no bigger than 100x100pixels nor bigger than 6k in file size--so no bitmaps--put it into a jpg file and it should be small enough then.
If you need to resize a pic. Here is a handy-dandy software program. It is called "irfanview" Just look at the other avator post here on this forum and it explains how to resize pics.