Christianity and being saved in Christ is a process. The longer you stay, the more you grow, the older you get, the relationship with Jesus solidifies and matures.
The change comes about by being in contact with God and having a true relationship and closeness with God. You can’t help but change.
The Holy Spirit within you helps you to conform and transform. Your life, your practices, your whole being will consistently say, Yes Jesus, I will do your will.