Put it in a cool spot in the apartment. If it is not cool enough, try a fan, air conditioner. You can also do a search for "swamp cooler". In simple terms, you wrap the carboy in a towel or shirt and place it in a water (cooler or pan). The evaporating action of the water will lower the temp of whats in the carboy. You can also rotate frozen water bottles in the water to cool the water more.