An aggressive cockerel is serious. You need to make a decision about what you want to do with him. He's only going to get worse from here unless you intervene. There's a very real danger of someone ending up with a serious injury involving a trip to the ER and stitches. I've seen a neighbor with a six inch scar from being spurred by his rooster.
You have three options, two of which involve being responsible, the third is to do nothing and be irresponsible and suffer the consequences.
You have the option of getting rid of the cockerel, either butchering him or giving him away.
Or you can keep him and discipline and train him. This involves commitment and work. It will require you to segregate the cockerel so the pullets will be safe as well as any humans that might come near him.
This training sometimes takes months before you see results, and there's always a chance the training won't take, that the cockerel has genetics to be bad. There are lots of great tutorials on BYC on how to discipline a rooster if you decide you wish to keep him and try this route.