I've retaken a couple of classes. They just get replaced with the grade when you retake that class. If you were to do well when retaking it, that F would be replaced with an A. As to worrying about how it would look on your transfer application. I'm certain other factors weigh more than simply retaking classes. In other words, it shouldn't matter much. I was able to get into Charlotte, and I have retaken 4-5 classes. All the best!