Spoiled gallery

I’ve just logged in to add to a gallery I created several years ago and found all images in all separate galleries. I don’t know if it has been like that for a while or I’ve pressed a wrong button but I can’t recall how I created this in the first place. I mean, how do you delete photos that are in the wrong gallery? Why are they in the wrong gallery? What’s an album and what’s a gallery?… It was such a simple update I had to do!

The page I need help with: [log in to see the link]