‘This means that anyone who belongs to Christ has become a new person. The old life is gone; a new life has begun! And all of this is a gift from God, who brought us back to himself through Christ.” 2Cor 5:17 NLT
As soon as you come to Christ, as soon as you ask Him to be your Saviour and Lord, your new life begins. You might not feel much different or look any different; you might not even behave any differently straight away. Yet you are now a new person.
Discipleship is the development of new ideas and new behaviours born from the new life already inside you. You change on the outside, because you have been changed inside. Your new behaviour does not bring you new life. That would be putting the cart before the horse. No, your new behaviour comes from the new life given by God.
The old life has gone; you just need to learn to let it go. Now you are a child of God, you need to let His Spirit gently show you how, and give you the strength to learn to be different than you were before. He will help you deal with old habits and give you new ones. He will set you free from old addictions and give you new desires.