How to log out of icloud on one iPhone only?

So my sister got an iPhone 4S and I have an iPhone 5, I wanted to know how I could log out of my icloud on the 4S without deleting everything on my iPhone 5 because I get her messages and she gets mine and it's so irritating:/

Settings>iCloud>scroll to the bottom where it says "delete account".

I would recommend just making a new apple id account for yourself so you can still use iCloud. You can still be logged in iTunes with your current apple id, just use your own apple id for everything else.