How can a Christian not sin?

Being human, you are going to sin. Being a Christian just makes you want to try harder not to sin. Being a Christian makes it so that you are forgiven by God's Grace if you ask for his forgiveness. If you intentionally sin, God is not happy. God is in you when you have that personal relationship with him and you invite him into your heart. Because Jesus died for your sins, as well as all of our sins, this guarantees that you will go to Heaven.