Remove image from post without removing from library

Hi! I’m using the Spun theme as a portfolio site for my jewelry. I have it set up so that each post is just thumbnails of jewelry. You click on the thumbnail to view a large pic with information about the piece. When I created the posts, sometimes the images appeared in the text editor section, and sometimes a big illustration representing a gallery showed up instead. I don’t know why. But now I’m doing SEO, and the images that don’t show up individually in the editor don’t show up in my sitemap. I thought I could just remove those galleries and repost them, but I seem to only be able to remove them from WordPress entirely then re-upload them. If I do that, I’ve wasted all the time I’ve spent on SEO for each image. This is something I feel like I will need to be able to do moving forward, and the only info I can find in the forums is ancient and doesn’t solve it. Any ideas??? Thanks!
fosbinderjewelry.com