Easy, by killing yourself. That is what baptism symbolizes. The spiritual event of being born again has the real effect of making you die to sin and die to self and this is what is pictured in baptism.
We don't literally die to sin, since we still continue to sin. We are no longer BOUND to sin, we are no longer under the sway of sin, the slavery of sin, we now have a new guiding principle within us, the Holy Spirit:
Likewise also reckon yourselves to be truly dead unto sin, but alive unto God in Christ, Jesus, our Lord. Therefore do not let sin reign in your mortal body that ye should obey it in the lusts thereof. Neither present your members [as] instruments of unrighteousness unto sin, but present yourselves unto God as those that are alive from the dead and your members [as] instruments of righteousness unto God. So that sin shall have no dominion over you; for ye are not under the law, but under grace. What then? shall we sin because we are not under the law, but under grace? No, in no wise. Or know ye not that to whom ye present yourselves servants to obey, his servants ye are to whom ye obey, whether of sin unto death or of the obedience unto righteousness? Thank God that, although ye were the servants of sin, ye have obeyed from the heart that form of doctrine unto which ye are delivered; and freed from sin, ye are become the servants of righteousness. Romans 6:11-18
As you can see, Paul tells us we are now no longer slaves or servants to sin. He doesn't say we CANNOT sin any longer, he says we SHOULDN'T sin any longer because we have a new "master" to obey. We are now servants of righteousness - and a servant is EXPECTED to obey their master. We are praised for being a good servant when we obey, but that doesn't mean that we cannot be bad servants who will receive a beating for disobedience.
The old man continues to live, as Paul mentions in the next chapter of Romans. We STILL fight against sin - but we are no longer its servant.
Regards