OK, it worked! Thanks leilady!
And by the way, I didn't need to put it on my desktop - I just did it in "preview" mode.
(But I'm kind of disappointed it took so many steps ...Macs usually don't require such shenanigans to do anything...that's why we love them. And then if I want my original photo to be back to its original size I have to go back in and change it back? There has to be an easier way.)