How do you change a rocker gasket on astra 1.6 54 plate?

To change the rocker gasket on a 2004 Astra 1.6 (54 plate), first ensure the engine is cool and disconnect the battery. Remove the engine cover and any components obstructing access to the rocker cover, such as the ignition coils and wiring harness. Unscrew the rocker cover bolts and gently lift off the cover, taking care not to damage the surfaces. Clean the mating surfaces, place the new gasket in position, and reassemble everything in reverse order, ensuring a proper torque setting on the bolts.