How do you change glow plugs on a Citroen Xsara?

To change the glow plugs on a Citroen Xsara, first, ensure the engine is cool and disconnect the battery. Remove the engine cover if needed, then locate the glow plugs on the cylinder head. Use a suitable socket to unscrew and remove the old glow plugs, taking care not to damage the threads. Install the new glow plugs by hand to avoid cross-threading, then reconnect everything and the battery.