How much time should i spend in a gym ?

your face will change as your body does. keep doing what your doing and then add some to each workout each month (or week or 2 weeks, it depends). there's no magic number to losing weight even if you have a trainer or special doctor. do as much as you can without killing yourself. push your limits. once you lose the weight you want to, DON'T STOP, it'll come back quickly.