Recently i've changed my username and i closed osu and opened it to see if it changed in game. I was later prompted to log in and it wont let me. I've tried my old username and the new one, still wont let me in. It might just be that it hasnt updated or something but..
osu! version: 20170103.2 (latest)
osu! version: 20170103.2 (latest)