For 60 years I have studied this question addressed by Paul in Romans cc 5-8, but is not answered by most people I have read. But, here is my conclusion:

• My question has always been, “How big is the God we worship, serve, and follow?”
• Sin does not live in the life (the body and spirit) of the Believer, the Follower of Jesus Christ. 
• The old man was crucified with Christ on the Cross and everyone who chooses to Believe receives everlasting life just as our Lord expressed to His friend, Nicodemus. 
• And we are raised to walk in the newness of life with Him. However, anyone who does not believe in Him and receives this gift is condemned already.

• All things become new for everyone who believes and is a Follower of the Christ, correct? Of course. Everything has now changed…EVERYTHING. We, indeed are new creatures in Christ Jesus. The indwelling Christ and the Holy Spirit now transform our spirits and bodies. How does anyone think the old nature is alive and well, and residing in the same person as Holy God? Are you kidding me?
• Our problem as Believers is not sin, the sin nature, because this died, was crucified with Jesus on the Cross. No, Paul does not speak of himself as a Believer when he writes, “I do that which I do not want to do.” But, what does Paul do?”
• “I am crucified with Christ, but it is not I that lives, but Christ lives in me.”
• The Apostle clearly instructs us not to “be drunk with wine, but be filled with the Holy Spirit.”
• We are then admonished to “Put on the entire armor of God” each day.
• And where do we receive our strength to live this life of righteousness? We receive this ability from Christ, “I can do all things through Christ who strengthens me.”
• Finally, our struggle as Christians is not with sin that lives within us, rather that is on the outside of our person, but we struggle with temptation provided by Satan’s minions working to bring us down. Assuredly, these creatures are defeated foes following a defeated leader named Satan.
• God, as Scripture teaches us, will not allow us to be tempted beyond what we cannot bear.

Jesus is Lord.