You don't need to. To be honest you don't want to either I've been there and I hated it. I have four best friends and they are better than even 100 popular people. Don't try to change yourself to something your not just to be popular, it's not worth it.
Just be yourself.
What you need to do is to join more after-school clubs and try to chat with the people around you. Be nice, and find something in common so you can expand on that. In class, talk to the people around you, be friendly and look approachable. Don't be rude to anyone, and make sure those people won't have anything against you.
Also, when your friends tell you a secret or tell you about special events, don't forget them. Keep your lips sealed, and remember what those people do. Soon, you'll find that you have too many friends. (You'll need two birthday parties.)