Go to User control Panel.
Then click on "Profile".
Then "edit avatar".
From there you can browse your computer for pictures or paste a link or URL to where the picture is located. Then click on Submit and if the picture is correctly sized it should show up above your username.
Note: When in "edit avatar' you will see there is a maximum width and length pixel size limit, so make sure your pic is resized accordingly before you try to upload it or it won't take. I have found that if you save your picture in "GIF" format it reduces the overall memory size compared to JPG.