1. If you want to upload your profile picture or change the old one you should click on the Account Settings button and then Profile.
2. To upload a picture, you can just click in the middle of the Profile Image box. The upload window will pop-up and you can choose your picture. Recomended size is 150x150.
3. Remember to save when you are finnished with the picture upload.
4. If you want to change the profile picture you already have, just click on the Upload New button.
5. Click Save to save your changes.