Hi there and welcome! I changed your forum permissions, so that should give you a little more freedom now.
You may notice some weird stuff until you have 10 posts, but you can comment in the gallery to get that number up there quickly.
Here's a tutorial on saving for the gallery that might be helpful for you. You'll notice in the tutorial, it says to resize to 600x600 pixels, but that is outdated. You can actually now save at 700x700 pixels.
To delete a layout in the gallery, you should see a "photo options" box in the upper right hand corner just above your layout. I believe you can edit/delete from there (you may have to click edit and then delete it from there). I'd screenshot it for you, but I have admin options that will look different from your screen. So, I'm not entirely sure what you'll see there. If you can't delete them though, I'd be happy to do it or you.
Let us know if you have any other questions! Feel free to jump in!