Upgrade to??? It’s a dev. preview 1, not even close to worth looking for anything on a normal desktop…
There’s an update for it that came out recently but I did not try UE4 with that update. Originally there was no splash screen just a black box, and the Editor wouldn’t show up, but was running.
Too bad UE4 doesn’t start in ML, was thinking to help it out though, as ML is becoming SL of OSX, with SL gone. 