According to WebMD, some effective exercises that can improve rounded shoulders include the lateral raise, alternating front raise and prone shoulder extension. Performing these exercises for three sets of 10 repetitions improves postures and increases muscle mass.
WebMD explains that the lateral raise is performed by holding a dumbbell in each hand while standing with feet together and then raising both arms slowly toward shoulder height until a "T" shape is created. The alternating front raise is performed by holding a dumbbell in each hand while standing with feet together and lifting one hand in front while slightly bending the elbow. After completing of your reps, repeat with the other arm. Lastly, the prone shoulder extension is performed by lying face down with arms on the sides with palms facing upward and a dumbbell in each hand. The arms are then lifted up as high as possible.