Hi,
This a major problem and it must be sorted! At six months old your dog is a baby and it will only get worse and he is only going to get bigger, more powerful and more dangerous.
Putting a muzzle on him is vital.
This is so important that you must seek a proffesional at once to help you. There is no ifs or buts and any modification you attempt on your own may make the situation worse. If you can't afford proffesional help then I'm afraid you can't keep the dog. A puppy showing this amount of aggression is going to grow into a very dangerous animal. Even with proffesional help you may have to accept that the dog has a mental health condition that can't be controlled. Do not put this off! Act now to save a lot of heartache and certain future injury to other people. I repeat a puppy of this age showing this amount of aggression needs to be asessed by a profesional a soon as possible.