We usually play with the famous Descartes quote "I think, therefore I am" but we think sooooo much, we plan soooo much, we live soooo much on our minds, that if we actually were our thoughts we would be so many things! ...
That leaves us then with what we do as the defining key of who we are.
Have you played pretend? Pretend you're someone else and actually take it to the street, play that Oscar winning role at the supermarket, in a shop, or just wondering around. It's a curious experience in the sense that everything around you seems to change. And it's not just that people will treat you in a different way, but you also treat yourself differently. Your mood changes, the voice you use to either be sweet or bitter resonates inside, and you become a different person... and, tchan nã! your thoughts change... Not your core beliefs of course, but you'll question things within a different perspective.
So, change your behavior to actually change your thoughts.
So many other examples come to mind: people that turn vegetarian, when people start doing sports; when you meet new friends, when you engage in a course, etc... you change because you're learning through your actions. So ACT! Act on it or act it out!