According to your BMI, you are a very health weight at the moment. I don't think you should push it too much. If you lose a stone, you will borderline underweight at 18.8, which is absolutely terrible for your overall health and long-term health. What you do to your body now, will affect your health down the line also.
Don't do it. You are perfectly fine the way you are at the moment. You should instead, work on maintaining that.
Why don't you try some strength training to tone yourself up a bit?