The enemy has no ground to stand on when the truth of God's Word is applied to his deception. First through salvation. If you have never accepted Jesus Christ as your personal Savior, you do not have a defense against guilt. The only thing that saves us from an onslaught of guilt and condemnation is acknowledgement of our sins before God and acceptance of His Son's death as payment for our past, present, and future failures. Until you realize your need for a personal Savior, any attempts to remove permanently the stains of guilt and sin are in vain.
Salvation is always the first step to freedom.
The second step is to identify, if possible, the cause of your guilt. This can be a very difficult and painful process. Often, the Holy Spirit will make the source of guilt clear. Remember, God always convicts us of specific sins. Vague feelings of guilt are almost always false guilt.