First you Repent for you sins. Then you ask Jesus to Forgive you of your sins. Then you start reading your Bible and Pray. Find a Spiritfilled Church to go to. Not all churches are Spiritfilled find one that is either non-denominational or Pentecostal or Protestant Then here's the most important part that most so called Christians don't have a clue on. After attending church ask people that are Christians of that church to lay hands on you to receive the Baptism Of The Holy Spirit.
I'm perhaps not able to explain it properly, but I'm sure somebody will correct me if I get it wrong. Or you can always ask a pastor to explain it fully. As I understand it, if you really regret your past mistakes and sins, and if you are sincerely intending to change your ways in the future, then by praying and asking for God's grace (either through Jesus or "in his name") you will be forgiven your past because of the promise and the sacrifice that Jesus made so that you would be given that forgiveness. When you have done this, you will be starting over from that point onward. You will effectively be "born again", and start out again with a clean slate. Then it will be up to you to keep that slate clean. I hope i got that right, and that it helps. My religion doesn't focus quite so much on the "born again" wording, although the core meaning is essentially the same.
John 3:5 be born of the water and the spirit. If you are asking how to be born again, I am assuming that you have heard the Gospel (Good News) - that despite your wrongs (and not doing right) God sent Jesus His son, our Lord and God, as a propitiation for you. When you believe that (that is, not just mentally assent to it, but are moved to active faith) in repentance (that is - changing now- from following Satan to following God) and confessing that Jesus is the Son Of God you are immersed in water (to enter into Christ) and come up a new person spiritually to live for Him.
Ephesians 2:8-9 states, "For it is by grace you have been saved, through faith-and this not from yourselves, it is the gift of God-not by works, so that no one can boast." When one is "saved," he/she has been born again, spiritually renewed, and is now a child of God by right of new birth. Trusting in Jesus Christ, the One who paid the penalty of sin when He died on the cross, is what it means to be "born again" spiritually. "Therefore, if anyone is in Christ, he is a new creation: the old has gone, the new has come!" (2 Corinthians 5:17).