Nepolean said;impossible can't be found in my dictionary.we need to have strong decision,desire,enthusiansium and so on.if u want to change something,u can change everything .i think desire is most important in everybody life.if u have strong desire to change character,why not change character.
I strongly believe that everybody can change his character. What we call character or personality is actually that part of your true self, which we project into our environment. I think that people consist of much more than they know.
If you concentrate on your inner self well enough, you would find a lot of new and aspect in yourself, which is also part of you. But because you never discovered them - at least up to now - you never prjected it into the outside environment, hence nobody thought of it as part of your character or personality.
Imagine how much people would think that your character changed, if you concentrated on your inner voice over months and didn't let your concentration distract by any other issue. I am sure, you would find a lot of new aspects, which would completely change your perspective of how you observe life. Thus your behaviour would change and people would recored a real change in your character.
Here you can read several articles about how personality can be changed. As you all know, the first and crucial aspect is DECIDEDNESS :)