More info, please
How old is the puppy?
How long have you had him?
Where did you get him? What were his conditions like before coming to live
Are you saying that he used to behave one way, and now he has changed?
If so, has he seen a vet?
Is he neutered?
Any changes in the household?
Also, you might be more specific about "attitude." Guarding the crate or sleeping place, for example, is pretty common and not much to worry about. Same with guarding toys, although you have to work with the puppy on not biting and on giving up things he is not supposed to have.
Finally, you're going to hear from people who are a lot smarter than me that the whole "alpha" dog thing and being the pack leader is a myth. It's not something I ever bought into -- except for when walking the dog. But, on the advice of others here, I abandoned the idea that I had to establish myself as pack leader, and I've had no problems establishing rules (well, no serious