Image Problems – controlling/installing

How does one remove duplicate images from a Portfolio page? When I am trying to upload images, if I try to delete one it looks like I have deleted the entire Gallery because “Preview Page” shows no images. But then after repeating the entire process, when I show “Preview Page” I have two copies of almost all images. How do I edit the page?

Also sometimes when I upload images, they show up in the Preview Section but not on the Website!

I would appreciate some guidance on how to make this program do what I want!!