What Breed Is My Dog?

My dog's paper work says she is a Pit Bull, but now that she is older she is starting not to look like one. What do you guys think? When she was a very young puppy she did look Pit Bull and sometimes now she still does, but only when her long ears are pulled back. I am not sure if I should change her paper work since she is looking less Pit Bull, but she must have some Pit since she looks like one at times. It is the same dog in the pictures, one is with her ears at rest and the other when she is happy and alert.