Crucified With Christ: Identity in Galatians 2:20
Paul does not offer a method for self-improvement. He describes a change of ownership: the self that ran his life was crucified with Christ, and the life he still lives in an ordinary body is lived by faith in the Son of God who loved him and gave himself for him.
2 Corinthians 5:17: New Creation in Christ
Second Corinthians 5:17 does not tell you to become a new creation; it says that in Christ you already are one. The verses around it show that this newness is God's reconciling work, received before it is performed.