It can be very difficult to “unteach” bad behavior. If you want your puppy to appropriately greet guests, it is best to teach your puppy what is expected of him when he is greeting people.
One method is to teach your puppy to sit-stay when you return home and only then do you reward your puppy for appropriate behavior. When you are expecting guests at your door, have your dog “sit” before you open the door. If your puppy understands that treats come only when they “sit” at your and other guests’ arrival, they will learn to sit and not jump.
Another method often suggested by trainers is to completely ignore the puppy if they are jumping and simply walk into their space.
In my experience, rewarding the behavior you want is the quickest way to get the desired behavior. Don’t reward a jumping puppy by petting them or paying attention to them when they are displaying inappropriate behavior.