I applaud you wanting to make changes. I'm an introvert who doesn't want to be an extrovert - but has lived extrovertedly for quite a bit of my life.
Visit places you don't normally go. This could be a party, a bar, a restaurant, any place that's social. Then, don't worry about pushing yourself...usually the natural extroverts will help you out. Then, just talk. If it gets too stimulating, excuse yourself either for a few minutes or leave for the night.
You start by pushing beyond your comfort zone. Maybe comfort would be reading, not posting, just observing. If you want to interact, post (like you did here), talk, attempt contact. Works online, IRL, you get to choose how much you can handle.
And maybe one venue doesn't work so well for you - maybe a bar is just too much. Try a library to start.
If you know what your normal introverted behavior is, you can then decide which behaviors you want to change. Sounds silly. But sometimes those little, simple things will help with the biggest changes.