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Exercises for fixing a hunchback:

Upper back foam rolling to increase the mobility of your upper back. Lie on a foam roller placed in the middle of your back and perpendicular to the spine. With your face facing upwards, keep your hands behind your head and bend your upper back over the roller five times.  You can repeat for each segment of your upper back by adjusting the roller.

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Superman to strengthen the weak muscles on your back. First, lie with your face down, arms on the sides, and palms facing down. Slowly lift your chest and hands off the floor, stretching as far and as high as you can while pressing your shoulder blades together and keeping your chin down. Hold this position for eight seconds. Do this eight times. Repeat two to three sets daily.


Withhold
a good posture.

When standing: keep your chest high, your shoulders back and relaxed. Try not to tilt your head forward, backward or sideways. Instead, tuck your chin down slightly and pull your head back and up as if your neck is against a wall. Make sure your knees are relaxed, not locked. Keep your feet parallel and your weight balanced evenly on both feet.

If you're standing for a long period of time: alternate between leaning on your left and right feet.

When sitting: have your back firmly against the chair. Your feet resting flat on the floor while keeping your knees level or a little lower with your hip. Keep your upper back and neck comfortably straight. Avoid leaning forward.


Sources:

http://www.pinterest.com/pin/16607092349809066/
http://www.barstarzz.com/howto/superman-lower-back-exercise/
http://health.india.com/diseases-conditions/top-5-bad-postures-that-can-affect-your-health/