like this http://www.auslogics.com/en/software/duplicate-file-finder/ to find duplicate files and then choose to delete them. In terms of deleting duplicate files and keeping only the best quality ones, I wouldn't consider those files to be duplicate, because they are not exactly the same.
that will automatically find all the photos on my computer and delete all the duplicates and keep only the BEST quality ones? I am NOT computer-savvy at all. I have about 15 years worth of family photos on my computer, mostly of my 3 kids & 5 grandkids. So I'd estimate maybe 20,000 photos, but at least 1/3 of of them are duplicates. I have Windows 7.