How to train my dog not to be aggressive with other dogs?

I have a dog (8ball) he is a retriever mix and about 10 months old. I have been trying to walk him but every time we run into a dog he tries to attack.

I turn around and try to go the opposite way but he just pulls and growls. I really want to be able to take him to the dog park and let him play with other dogs and play fetch at the park instead of our small backyard.

What can i do to train him to be more friendly with other dogs.