On the top right of this page you will see SETTINGS.
Click that then go to MY SETTINGS on the Left (My Profile).
Under that you will see Edit Avator, Edit Profile Pic, Edit Signature, etc.
The signature is the Quote or whatever that attaches to all your posts at the bottom. The Avator is the pic next to your name on all posts. If the Pic file is too large you might have to shrink it.
Hope that helps.