There are a few parts to this. Firstly image versions are grouped together into repositories - you’ll see separate repositories for your Nginx and simple-web images. There are AZ commands to work with repositories.
Each repository can have multiple images with different tags - 6.0 and latest are the tags for the simple-web image. You can list those tags with the CLI and sort them by creation time.
Then to delete an image you need to use the full name - registry domain plus repository plus tag.
Need more? Here’s the solution.