You can try self regression, its a technique that uses visualization and a deep trance. But it is within my own experience that I suggest people do not delve into past existence until they have a firm sense of identity as well as a strong security in their present life.
Teens especially are "finding themselves" and going through an identity crisis of sorts. On average, people do not have a firm confidance as to who they are until they are between the age of 18 and 23 depending on the individual.
If we naturally remember that is one thing. I for one had dreams of my past lives since childhood. And a few spontaneous memories during meditation as a teen. But it wasn't until I was 19, married and planning for a child that I felt ready to regress. Even then, what I have experienced has changed me. But my strong sense of identity prevented me from gaining negative traits due to it.
Yes! I have witnessed many people who, against my advice delved into their past too early and they are complete emotional and mental recks. One life is enough to deal with, by learning about your past lives, all emotions and thoughts flood back and if you didn't deal with them then, you'll have to work them out now or you'll suffer from their influence.
So please be cautious.