The best approach is to put in an exhaust fan, the ducting for which would discharge outdoors. Through a roof, through a wall, through a soffit..

Guideline 26: Ventilation http://starcraftcustombuilders.com/bath.design.rules.htm#.WwbIg_ZFy8z

You can start by seeing where that vent goes through. If lucky enough, opening the right windows/doors might permit natural ventilation to some degree.

If not, ceiling vent (preferably to the exterior and not just the attic) or through a external wall (if there is one).