How to train a somewhat agressive dog?

Ok, so I am trying to help my friend and training her dog since she's never had a dog before. He is a 11 month old lab Rottweiler mix. she lives with her parents who didn't train their dogs different things like sit and lay down and that's what I am doing with her dog since he is big and her parents dogs are small dogs like a small cocker spaniels. With her dog though, he hasn't been neutered and will be neutered next month because our vet said to wait until he was around ten months to help with his growth for neutering. So now my question, my friends dog has been going after the littler dogs like he's trying to be aggressive. more so now than ever. How can I train him to not try going after the little dogs and trying to be aggressive to them (he mostly tries biting them but not hard enough to break their skin an we get after him when he does.) First question, will he calm down when we get him neutered? And is there any suggestions on training him to be acting the way he does to the other dogs?