Hello ahickpoet and welcome to the Forums!
I have found your ad under Vintage Trailers
. Moderator privileges allow me to go in like I'm editing -- just as you would. Let us walk through this and see what we're both doing in common.
Have your pictures you want to upload ready before proceeding. I would suggest modifying them in any photo program preloaded on your computer. When modifying an original digital photo, be sure to do a 'Save As' or your original file would be erased if you only do a 'Save.' When I'm doing a 'Save As' I save it to a temporary desktop file I'll discard after the item is sold -- this makes it very easy to find when you do the following steps. They should be jpeg format (not tiff or bitmap) -- 800 x 600 is a good size. This fits within the Forums file size maximum which may be 840 or 860 pixels wide -- if memory were serving me better.
1. While you are logged in as yourself open your ad from the link above. Just below the zip code entry area is a dark blue bar with words 'Edit Ad' -- click that area and open the edit window.
2. See "Select new images or leave blank to use current one" area partway down the edit window. You can add up to six photos to your ad. Click "Browse" to add picture 1. From the resulting popup window, select the location of one of your edited photos you wish to add.
3. Add additional photos as needed.
4. I would suggest adding the model year to your "Edit title for the item" line.
5. Be sure to click 'Submit Changes' at the bottom before leaving that page.
Post back to this thread if you have any problems and I'll pick up on it tomorrow. Good luck!