There is no such thing as a 13 wks old puppy being aggressive. So get that out of you mind now... There is a dynamic that you can set up, or avoid which is greatly preferred, which creates an atmosphere of conflict...don't do that! Your little puppy is a baby..like a 2 yr old child. No reasoning with them when they're tired and need a nap, you just put them down for a nap! Quietly and without emotion or conflict.
Behavior that you don't like is discouraged, behavior that you like is encouraged...not rocket science!
Just remember, your job is to LEAD your puppy into the behaviors you want to see, while ignoring them and their misbehaviors while getting them there....it's a marathon not a race. Puppies will be puppies, just be fair and patient, they do grow up...
I just wanted to expand on this a bit. I agree with everything Tim said and it is the basis for why I don't "train" puppies.
I am a firm believer that dogs, like children, learn what they live. If you raise a pup with emotional, aggressive actions that is what it will learn and how it will react to any given situation. And you cannot reason with a dog anymore then you can with a toddler, they just don't get it.
Puppies in my house spend their first months learning me, they learn what pleases me and what doesn't. To do this I praise what I like and ignore what I don't. I expect biting, chewing, ankle shredding and outbursts. I just don't reward them with attention.
I think that putting a ton of pressure to learn on youngsters impairs the relationship, so I go out of my way to make sure that I am setting up success. I don't like being jumped on so I not only don't touch jumping puppies, I try to stay at their level when I am interacting with them. I crouch down to pet them and speak to them, I remove the need to jump up. I don't want my puppies learning to pee in the house, so I don't let it happen. When removing from crates I scoop them up and carry them outside. That way when they pee from excitement it's outside, and I can praise it. I dislike barking and fussing so I set naptimes before they get wound up and cranky. I don't like my belongings chewed so I limit access to rooms and keep the room we are in free of anything but toys at floor level. My whole set up is designed to minimize confrontation and remove the necessity to do battle, and I don't get mad at puppies for being puppies.