How do I become a Christian?

Admit
Admit to God that you are a sinner (Romans 3:23; Romans 6:23) and repent of your sin (meaning turn away from) (Acts 3:19; 1 John 1:9)

Romans 3:23 -- for all have sinned and fall short of the glory of God.
Romans 3:23 -- For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
Acts 3:19 -- Repent, then, and turn to God, so that your sins may be wiped out, that times of refreshing may come from the Lord
1 John 1:9 -- If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteous

Believe
Believe that Jesus is God's Son and accept God's gift of forgiveness (Romans 5:8; Acts 4:12; John 3:16; John 1:11-13)

Romans 5:8 --But God demonstrates his own love for us in this: While we were still sinners, Christ died for us.
Acts 4:12 --Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved.

Confess
Confess your faith in Jesus Christ as Savior and Lord (Romans 10:9-10, 13)

Romans 10:9-10 -- That if you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead,
you will be saved. For it is with the heart that you believe and are justified, and it is with your mouth that you confess and are saved.
Romans 10:13 -- for, "Everyone who calls on the name of the Lord will be saved."