It's a misconception that neutering/spaying a dog will make them calmer. Most dogs will feel slightly different, more mellow and less active immediately after a treatment or surgery at their vet.
However with time each dog will start behaving and feeling like their old selves again. Instead of relying on this procedure to hopefully calm or relax your dog, look for safe and fun games and activities for them to do on a daily basis. Everything from dog food puzzles, snuffle mats, tug and pull toys to agility training will help ensure you have a calm and relaxed dog at home!