You don't have to stop doing your aerobics to add resistance training -- in fact the two go very well together. As for diet, while added protein can help someone who is trying to build muscle, don't overdo it and don't start eating unhealthy foods to get there, such as dairy -- most people really don't digest it very well. Don't neglect your balanced diet, vegetables will always be the most important nutrient sources in a diet, but it is true, adding protein to a resistance training program will probably speed up the building of muscle. But hard work is the biggest factor. Always put health above looks. Good luck.
definetly eat a very high calorie protein diet if your looking to build nuscle not fat then i recomend working out your muscle and afterwards drinking a protein shake with things like milk,peanut butter, and banana make sure your eating healthy fats and lots of protein