If you do not believe in Jesus, Repent (change your mind) about your unbelief and believe in Jesus.
Repent means “change your mind.”
The pagans in Acts needed to change their minds about their idols (that they were not to be worshipped) and believe in Jesus alone.
The unbelieving Jews needed to change their minds about their unbelief in Christ and crucifying Christ and believe in Jesus.
Natural prideful people need to change their minds that their good works (“dead works”) count for salvation and believe in Jesus.