For the Minky Momo, I change it to this one instead because it's bigger. For Samurai 7 and Saint Seiya, I did approve your Kisara and Saint Seiya anime screenshots which changes the default image. BigHeart711 and I mentioned a few times already. Whenever you upload new caps, it will change the default image.
For me, I usually change the default image when I'm done. It's better to wait when you're done. Or you can accumulate 5,000 wiki points and change your images whenever you like as long as you do it according to the rules.
I changed everything except for God Mazinger since I have trouble finding a better and bigger image to replace that one.