How to change he icons on my iPhone?

Okay I saw that some of my friends can change icons like fore Facebook they can make it cheetah print or they can change their Instagram app into purple. How do you do that? Is there an app?

You have to jailbreak your iphone to do that if you don't know how here are the steps:
also do it at your own risk! Not my fault if your iphone breaks

They jailbroke their iPhones in order to do that.