Ahsan,
I might be wrong, but boring throttle bodies is normally for removing the taper from 37 to 35 mm. That is to say, your TB will be 37 mm through and through. I don't think you can go higher as your butterfly will not fit properly.
What car do you have? It might be possible to swap a bigger throttle body and recalibrate the ECU. Although, I think you'll need to recalibrate the ECU anyway as your mixtures will probably lean out at full load because of the increased airflow with your TB mod.
Drive safe!
Sami