How to gain more muscle ?

The basics: You will likely have to eat a little bit more than you are now, and most of the extra calories should be from protein. In addition to that, you will need to start some sort of resistance training. Pick something that you enjoy. Hope this helps!

Eat & exercise.: You need to focus your exercise regimen more on weight training than aerobics. Work out with heavier weights and fewer reps per set - around four reps per set. Keep good form with your exercises to minimize chance of injury. As well, make sure you eats lots of food, and focus on complex carbohydrates and lean protein sources.