Hi Sylvia. Dan from Trulia here. If you want to edit the photos for your listing or edit open house times, you can do this straight from the My Listings page.
The messaging that says "pro only" only refers to being able to change the listing source (which would make it so that users wanting more info on one of your listings would be directed to the site of your choice). This is a feature offered only to Trulia Pro customers (more info at the link I've provided).
Of course, it's possible that you need to edit something else associated with this listing (e.g., price, description). We get your listings from mlspin, so the best way to get any of this info changed (i..e., anything other than open house times or photos) would be to update the info there.