How does one who’s very shy become an extrovert?

Shy and introvert are not the same thing. Being introverted just means that social interaction drains your energy, not that you're afraid to be social or that you don't like being social. For example, Jim Carey is an introvert, but you wouldn't say he's shy, would you? I don't know how to fix shyness, but you can't change whether you're an introvert or extrovert. However introverted/extroverted you are when you're a toddler, that's how introverted/extroverted you'll be when you die no matter what you do.