If you log in on social.redlightcenter.com you should get to your profile with a row of black buttons near the top, one of which is My Pics. Within that, you have current pictures displayed, and each has a check box. There's a big "upload picture" button if it's not full, and that will let you grab one off your computer and add a caption, and you can tick one picture's box and choose action "make default" from the pull-down menu in the top left.