I am a bruiser wishing to become a brawler.
Brawlers are either Monks or Bruisers... you cannot change from your actual class of Bruiser back to a Brawler, since it's not a playable class. Monks are restricted to good aligned players only, Bruisers are restricted to evil aligned players only. If you want to switch from Bruiser to Monk, then you would need to go through the Betrayal process for your city to change to one of the good aligned cities instead (which at level 10.. it's just easier to start over).
I think you're just simply misunderstanding what your class should be, since it's an older character that probably never got forced to choose their class back in the old system that Calthine mentioned. It sounds like you are already the correct brawler class of Bruiser. :)