1) Decide who you want to be.
2) Start by changing how you look. Dress like who you want to be, wear more/less makeup. Change your shoes also. Change your posture, if necessary. Get a haircut, dye your hair, wear it up or down. Paint your nails, or take off the nail polish. The smallest things can change how you look at yourself. This will help with #3.
3) Act like who you want to be. Treat people differently. Don't tell people you are reinventing yourself. Instead, act like you have always been this way. Though, sometimes close friends can help with this. It will be really hard, but if you keep reminding yourself, it will get easier. Don't quit when you mess up once. Just take a deep breath and remind yourself who you are. If you can, you could also try going by a different name, like your middle name or your nickname.
4) Don't worry about other people being surprised by the new "you". There may be some initial surprise, but if you act like you haven't changed, that you have always been that way, then they most likely won't bother you.
Hope you find out who you are, and hope I helped.