This will require you to improve your posture. But, do work on your posture as standing up taller can make you look 5 pounds slimmer. Stand in such a way that your pelvis is relaxed. You can also stand against a wall to check whether your posture is straight. Make sure that your back is pressed up against the wall with no more than an inch between the wall and your lower back. A wider gap means your pelvis is not straight.
If you want to build muscle and burn fat at the same time, you have to perform circuit training three days per week. How can you achieve this? Indulge in full body exercises like lunges, push-ups, and pull-ups, for one set of 15 repetitions. Don't forget to follow every exercise with one minute of jumping rope. You should be able to burn around 500 to 600 calories per workout.