Close encounter
Some people change in a big way almost overnight and others change gradually over time. In both cases, there is always something that triggers the change. And the change lasts when the trigger touches the core of the mindset. It cannot be "transactional" - this is not enough to sustain the change long term.
A changed life starts with a heartfelt decision to devote my entire existence to God. And that decision is triggered by a close encounter with God himself.
The shape of the encounter differs between person to person. If you have not encountered God, seek him. He is never far and he is waiting for you.