You have to sign in to your account (It should say Web site pages near the top middle)
so start at your storeadmin page.
Then go to the top left where it says pages and click on it.
On the left will be listed links for the pages. One of them should be "Gallery." To the right of that should be a button where you can "edit" the gallery. That is where you can take pictures out.
I use drag and drop to put the pictures in there. It makes it easier!