You can't pick your personality, however you can expose yourself to new things. Meet new people. Read books on topics that you've never read about. Learn things and form opinions, but never be afraid to change your opinion or admit that you're wrong. Look at art that shows a different perspective. Listen to music that you've never heard. Write. Draw. Act. Fight. Love. By doing things that are new, you'll be able to find out who you are. But don't be surprised if who you are is who you've been all along.