Click on "Settings" at the top right of the screen. On the left side of that screen is a menu list. Near the top, you will see a line that says "Edit avatar". Click that. You now have option 1 (link from a website) and option 2, upload from your computer. Click on the Browse button and find the picture on your computer. Click on the file to upload it. Note that the picture has to be pretty small (120 x 120 pixels or 9.8K max for Platinum, I don't what it is for Gold).