@melissabales you will need a display assembly. Follow something like [https://www.youtube.com/watch?v=6KV7rQrSJZQ|this video] or if you need something less descriptive, use [https://www.youtube.com/watch?v=PajspDgw5LY&pp=ygUgU2Ftc3VuZyBHYWxheHkgUzIzIFVsdHJhIGRpc3BsYXk%3D|this one]
That was the easy part. The hard part is to actually get a new replacement. Those are AMOLED displays and they are very pricey. So do an online search and see if there is a vendor that appeals to you, but buyer beware.
While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.