Instead of deleting them - why don't you just edit them - delete the picture and add a upload the new one.
Lilian, could it be you are uploading a small picture? Too big and it won't upload at all, very small and you can't enlarge it?
I hope it works for you but do not let it bother you. I was just going to get a closer look since My eyesight has gotten so bad! I am sure you will get it worked out! Hugs, Linda