The Scripture say the heart is deceitfully wicked who can know it and warns us to crucify our flesh daily; while at the same time tells us we fight against not flesh and blood but against principalities, and powers and rulers of the darkness. Either way only G-d can deliver us and make us more like Him.... So, would you just rather be evil in the heart or oppressed by a demonic spirit? How do you know which is which? (I hope this is the right which, I did not look it up).
Interesting so the human heart is only deceitfully wicked before salvation.... So sins like pride and envy, or jealousy, disobedience, is because you are demon oppressed? How do you not sin; how are you free from you oppression?
The heart that is wicked and deceitful is the carnal flesh, the heart inclined to walk in its own understanding not believing God, as opposed to the pure in heart who do believe God and are surrendered to the Spirit of Jesus Christ.
The “flesh & blood” we’re not fighting against is other people. It’s wicked spirits of the world that are our enemies. Those spirits may be operating through people, or through circumstances. But the Lord tells us to fight spiritually, through fasting and prayer, and having done all, to stand on the Word of God.
"Not by might, nor by power, but by My Spirit,” says the LORD of hosts.
As to your question, "How do you not sin?", there’s only one answer. Jesus washed your sins away so that you can now live in truth and righteousness. You may as well believe Him and walk set free. If not, you’re wasting your time and your life believing a lie.