iPhone 4 and iPhone 4s swap??

My wife has a iPhone4 and I had a iPhone 4s. I have switched to a Samsung S III and want to give her my old iPhone 4s. Now she has a lot of pictures, music, etc. as do I on my old iPhone 4s. How do I backup the iPhone 4s completely with all my notes, pictures, music, etc. then reset to factory settings. After this, I need to make sure her iPhone 4 is also completely backed-up with all her pics, music, etc. and then put all of her stuff on the iPhone 4s and give it back to her with everything she had on her old iPhone 4?? I'm sure it's a lot easier than typing all this information here but I don't know how to do it and if you call AT&T over the weekend, I'm sure I'll get someone who doesn't speak english!!! Please help!!