Change primary image, delete older

Hi. I originally added a teaser image but it was the wrong one and I have since uploaded the correct version (original upload was an early draft with a short stem on the cherry, new version has the correct longer stem). 

I would like to delete this one https://www.imdb.com/title/tt37200419/mediaviewer/rm3545815810/

and set the other image as the primary. I do not see the option to delete the old image after following the guides for how to do so.

Any help is appreciated, thank you! (Hi Maya!)