You have 12 hours after your initial post to edit. After that you have to contact a moderator (tiny "Contact Us" link at the bottom of every page).
It would be easier to add your pictures to a new post in the same thread.
Attaching pictures is not exactly intuitive. Directions are in post #7 here:
http://www.fiberglassrv.com/forums/f...ics-43021.html
Best wishes with your sale!