After you sign into your account, you will click on your listing 'edit listing' and scroll down until you reach the photos. They should give you an option to remove current photos by clicking on the X, and upload new photos. Make sure you hit 'done' when finished so it saves your work. I have found that when changing photos on Zillow and Trulia, it takes 24 hours sometimes for the new photos to appear. You may have to reorder the photos when they appear as well. New updated photos do make a big difference, you are smart to change them out. Good luck!