How many calories should I consume a Day?

I'm 19 years old, I weigh around 135 and about 5'8". I've been doing P90X every other day in this order: Back and Biceps, Chest and Back, Shoulders and Arms, Shoulders and Chest, and I keep following that cycle (I don't really pay attention to the other workouts in the program). I am looking to build more muscle out of it. My friend is telling me i should be eating around 4500 calories a day, but I think all that's going to do is give me a gut. I currently have a small layer of fat over my stomach which i've been trying to get rid of too(I've also been doing Ab Ripper X on all of my workout days). So I was just wondering how many calories I should be eating a day. I also take a gl of Muscle Milk after every workout.