Yes, you can perform yoga to reduce your breast size. But remember that you need to lose weight fro all over your body to achieve the desired effect on your breast. Power yoga is an excellent yoga method for reducing breast size. In power yoga, weight loss is rapid as it is performed in a hot room and this induces lots of sweating and increases metabolism rate leading to weight loss. However you should keep in mind that your breast size is determined by genetic factors and the only way to achieve a smaller size would be to lose lots of weight which is unhealthy.