Step Four: Fight your professor
When your experience bar turns blue, you are ready to face your professor
Go to Classes and Training located in Hogwarts and your hometown, Ottery or Spinner's.
If you keep fighting, your professor will find you when you get to enough experience for two levels and it will cost you a portkey (which allows you to travel).
When you are ready, click “Challenge Professor” and you will gain a level once you defeat your master. If you are defeated, you must wait until the next game day to try again. (You won't die.)