How can I change the small picture of me that can be seen throughout the website?
You must be referring to the avatar. To change the avatar, hover your cursor over the 'Dashboard' icon (the black semi-circle) on the uppermost navigation menu, then click on 'Avatar' in the drop-down. On the right hand side in the 'Add New Avatar' section, click on 'Choose File' and browse to the image you want to add, then select it. Crop the portion of the image you like best and either check or uncheck 'Copy to profile photos album'. Then click on 'Add Avatar'.
If you would rather not add your own just yet then you can always choose an avatar from our ready-made selection.