replace heater core

need to change heater core in 1994 lumina car. I think the dash has to come out can anyone tell me if this is true and how to replace core?

no, not the dash, just the plastic panels under the dash. It's been a long time since I've done it but if you take the underside of the dash off, the heater core is right underneith the center part of the dash

thanks will try to find it