I don't know how to overcome the chicken heart in the front of lot's audience

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When i am a little girl , i was very silent wordless. Many adults don't like my temper for sometimes will burst out losing my temper . Because my heart loads much dissatifaction by the people around for my silent and wierd temper . Gradually i am very chicken hearted to make friends with others , not to mention to give the presentation before the crowds . But now i become a girl very sunny and talktive . Because i swear to change my personatliy when i am in my university . Many guys in my company like take me as their good friends . I was happy with that .But i can not overcome the fear-mood before lots of people . How can i make it and develop such confidence ? Can someone give me good tips ?