2003 Hyundai Elantra check engine light on

Hello im vincent, my check engine light came on . I have a obdII scanner, and it read code p0420. Catalyst system efficiency below threshold (bank 1). Does that mean i have to replace my catalytic converters. My vehicle is equipped with a dirrect exhaust manifold converter and a secondary catalytic converter , or should i replace both of the oxygen sensors. I hope you could give me a better opinion of what could i do. Thank you.