No one follows the Old Testament anymore. Or at least the vast majority does not. They look to the King James version instead.
The Jews follow the Old Testament.
Christians have The Old testament as a part of the Bible. We do follow the teachings of Old Testament, but not all of them.
Old Testament was a Old Covenent between God and man. It was based on fulfilling the law of God, a set of commands and laws. Otherwise, the man would die. But all this was never coming from heart, it was rather a external holiness. The heart was unchanged, inclined to do evil. It was a struggle.
But in the New Testament, Jesus Christ died for the sins of people. In the New Testament, to those who believe in Jesus, God promises to take their stoned and evil heart, and give them a new heart, a new spirit, whcih is good and "soft", with which we can fulfil the law of God by heart, from our heart, to love the law of god and to love God.
This new heart, this new life in Jesus Christ, is what Christians call "born again".