I John 1:9 “If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.”
Victory over sin cannot start from a denial of its existence in your life. It also is no good to generalize about sin: “If I have sinned, please forgive me.”
When you want victory, you first need to make sure you are a born-again Christian. Once you are sure of that, start your confession by naming that sin (or sins) to God and ask His forgiveness. Call the sin by its real name: lust, greed, pride, pornography, theft, drunkenness, envy, etc.
Once it is confessed and you truly desire to forsake it, only then can you have victory. Proverbs 28:13 says: “He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.”
God is more than willing to give you the victory you need. Tell Him you need His help and then believe He will give it. He will, but you may need to take some steps to ensure an ongoing victory. For instance, if drinking alcohol is your sin and getting drunk, get the alcohol out of your house. Avoid friends you used to drink with and stay out of bars and clubs.
If there is a problem in the thought life, God can help you with that, too. Listen to this promise in II Corinthians 10:3-5: “For though we walk in the flesh, we do not war after the flesh: (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;) Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ;”
Notice that it is not your strength that gets the victory – but it is His weapons and His power behind them. You know the verse in Philippians 4:13: “I can do all things through Christ which strengtheneth me.”
When you depend on your own power for victory, it will only be temporary and probably short-lived. God can give you an ongoing victory, but it must be an hour-by-hour dependency.