How do I retrieve deleted photos once deleted?

I went to Lake Manchester today and took some adorable photos of my brother and the lake and I made a folder with them in it called Lake Manchester. For some stupid reason, I wanted to delete them from Camera Roll thinking that they would still be in the Lake Manchester folder but then it came up with a Delete Everywhere button and I accidentally pressed it. Please help me get them back. They were the best photos I have ever taken!