Can we really change our body shape through exercise?
The short answer, unfortunately, is no. Our bone structure and proportions are largely fixed after we reach adulthood.
You can, however, target specific areas of your body to play with proportions. Be careful, lifting weights will not magically turn fat into muscle, and targeting certain areas of the body will not magically melt fat away from that specific place.
To lose weight, increase your physical activity and exercise, and eat well. Remember your smaller muscle groups. If you only run on a treadmill, you're only going to work the muscles used during running. Consider a boot-camp style workout, which will include oft-forgotten muscles, like those in your hips and wrists. Don't forget your core, targeting your back and abdominals is key to stability, which will help your form. And don't ignore your form! We're wired to avoid discomfort, so we're naturally inclined to use our larger muscles. Pay attention to which muscles should be targeted for the exercise you're doing. It might feel easier, but using momentum to do your reps may cause more harm than good in the long run. Remember to stretch! Stretching is key to maintaining a natural range of motion for all of your joints.