Green’s Dictionary of Slang

(orig. US campus) to change one’s life radically; to reverse one’s position.

1979		Eble Campus Sl. Mar. 2: do a 180 – to change completely.
2000		Guardian Weekend 27 May 8: I just said, let me do a whole 180 with my life. I don’t want to do any more negative hip-hop music.
2012		S. Blass Pirate for Life 69: Joe did a 180 and told me that the Pirates were sending me to Columbus.