Good for you for being nice! Talk to people, be friendly, smile, say hello first, and pitch in when someone looks like they need help. It may take a little time for them to see you've changed, but they will.
Good for you! Just try to talk kindly, and if someone starts talking about how mean you were, or if they want a fight, just walk away. They will eventually find out that your a nice person.. Good luck! :-)