We don't know who the headmaster is in 2017. We know from the foward of The Tales of the Beedle the Bard that McGonagall was Headmistress until at least 2008, but, in an interview after the release of Deathly Hallows in 2007, JKR said that, by the time Albus Potter attended Hogwarts in 2017, "someone completely new" would be the headmaster because McGonagall was "really getting on a bit."