The only way to make human arms bigger is by adding more muscle. Building more muscle requires consuming a surplus of calories and using resistance training to stimulate the muscle to grow in size.
Many different exercises work the arms. Perform curls or rows to work the biceps, while the bench press and standing press target the triceps, among other body parts. Wrist curls or hand-gripper exercises are helpful for enlarging the size of the muscles in the forearms. A high-protein diet helps to provide muscles with the building blocks necessary to fuel their growth. Peanut butter, chicken breast and nuts are examples of good high-protein foods. Fish and soybeans are also foods with high amounts of protein.
While there is relatively little debate about the proper diet for adding muscle mass, trainers embrace different philosophies regarding the best ways to lift weights to add muscle mass. Some trainers advocate performing a low number of repetitions with heavy weights, while others recommend performing a high number of repetitions with light weights. Others prefer isometric exercises that rely on holding static poses while under resistance. Regardless of the specific strategy employed, the combination of surplus calorie intake and resistance training are constant factors.