To repent means to turn, to have a change of mind. In the New Testament repentance means to turn from sin. All men everywhere are commanded by God to repent of their sins (Acts 17:30). God's longsuffering leads us to repentance (2 Pet. 3:9) as does his kindness (Rom. 2:4).
There is true and false repentance, "For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation; but the sorrow of the world produces death," (2 Cor. 7:10).
See also, "What is Repentance?"