When I finished high school, I was pretty much a socialist. Then (believe it or not), higher education started changing me when, in college, I switched to social sciences. In economics, my professor showed me the great advantages of free trade and how it lifted people out of poverty.
During my bachelor degree, I further saw how free(er) markets helped society, thanks to having half my professors being classical liberals.
My position was cemented when I read all those authors (Smith, Bastiat, Say, Mises)