I need to optimize images

I need to optimize images on my website and I am not an expert by any means, so I installed and activated the free trial of Smush. I can see that the plugin should smush any new images I upload, but I want to smush the images that are already on my website. I tried to do the directory smush, but I do not see my images in the directories that come up in the Smush process. I only see images related to various plugins, but not the images I have uploaded in the past. Then I tried to perform smush through my media library, but it does not appear that any changes are made after I press the smush button for an individual image in my media library. I would appreciate any assistance you may provide regarding this issue.