To gain, "victory over sin" means that Jesus Christ has broken the absolute legal and ruling power of sin over the believer, though a lifelong, internal struggle against remaining sin still remains until glorification.
Those of us who are in union with Christ, have been rescued from the condemnation of Adam. Romans 6 teaches that the "old self" was crucified with Christ so that believers are no longer slaves to sin.
A Christian can not reach a state of complete sinlessness or eradicate the sin nature in this earthly life. Believers still stumble and commit conscious sin. Christ’s victory is complete and unassailable. His resurrection guarantees that sin no longer holds ultimate dominion over those united to Him.
Victory is actively worked out through progressive sanctification. As the Holy Spirit works within a believer, sin's power gradually weakens, and the fruit of the Spirit grows. The more sanctified a person becomes, the more acutely aware they are of their remaining sin and failures.
Christians achieve daily ground against sin not by "letting go and letting God" in a passive sense, but through active spiritual warfare, repentance, reliance on the Word, and obedience driven by faith.