5 month old ACD being aggressive

Hello everybody I need your guys help. I have a 5 month old ACD who has been acting aggressive towards my family and I. He was friendly when we got him and around 3 1/2 months old he started to show sign of aggression. He is playful at times and lovable but then switches up and starts to act aggressive. He is very bipolar. When we come home from work or school he gets very excited to see us. Sometimes he lets out a little bit of pee due to excitement. When we need to take him out to go pee and put the leash on him he starts to growl and pull back when we try to walk. He doesn’t allow us to pick him up or pet him a lot. When he grabs something he’s not supposed to and we try to get it out of his mouth he try’s to attack us. He doesn’t get mad when he has a toy in his mouth and we try to take it away. He doesn’t take no for an answer. He very smart and knows all the basics (sit,paw,down,up,leave it, and roll over). We love him and want to keep him but his aggression is making it stressful for us. Most of the time he is with my dad on the ranch. He gets to run in an open field almost every day. What can we do to stop this aggression