If someone has realized that he made a wrong decision in life or has had the wrong beliefs for a long time, he might say I lived the wrong way. What are alternative ways of phrasing this?
It doesn't need to be religious.
Since this is a common sentiment within Christianity (and you did mention belief) here's some synonymous phrases you might hear in that context:
I was blind but now I see.
I was lost but now am found.
I strayed from the straight and narrow.
I strayed from the path of righteousness.
I am a prodigal son, returning home.
Forgive me Father, for I have sinned...
That's a very common line, haha :)
But normally, I would just say, "I made a wrong move" if I felt I made a bad decision.
People often say that they have reformed from something; e.g. "I am a reformed alcoholic".