Paul makes further reference to it in Eph 4 and there are a couple of things about it that are highly interesting.
20But you did not learn Christ in this way, 21if indeed you have heard Him and have been taught in Him, just as truth is in Jesus,
22that, in reference to your former manner of life, you lay aside the old self, which is being corrupted in accordance with the lusts of deceit,
23and that you be renewed in the spirit of your mind,
24and put on the new self, which in the likeness of God has been created in righteousness and holiness of the truth.
25Therefore, laying aside falsehood, SPEAK TRUTH EACH ONE of you WITH HIS NEIGHBOR, for we are members of one another.
26BE ANGRY, AND yet DO NOT SIN; do not let the sun go down on your anger,
27and do not give the devil an opportunity.
In between the believer taking off the old self and putting on the new is the renovation of the mind or where we do our thinking.
Notice that it says the old self, the sin nature is being corrupted. In the Greek this is a present passive. That means that it is receiving the action of being corrupted. Sometimes a present tense is just an event occuring in the present, sometimes it carries the connotation of repeated action but many times, as with salvation it views an ongoing condition. So our sin natures are constantly being corrupted by the lusts of deceit.
In order to quit living in the flesh and learn to live in the new man a believer has to have his thinking changed. Our thinking is changed by the Word. The more we learn under the filling of the Spirit, the more we are able to live in who we are in Christ.
Notice also, he says 'lay aside falsehood' and 'be angry and do not sin. He is talking to believers. Unbelievers will live in their old self. The believer has the opportunity to lay it aside. But, a believer who does not submit to having his thinking changed is going to live in the old man.