Use Prusa’s 23-step CORE One nozzle guide, not a procedure for the CORE One L or MK4. Prepare the specified tools and protect the heatbed before opening the Nextruder.
Unload filament, cool and power off. Remove the top cover and Nextruder parts in order, disconnect the named cables by their plugs and take out the hotend assembly. Keep every fastener organized.
Install the new Prusa Nozzle fully, route heater and thermistor cables exactly as shown and close the toolhead without pinching them. On startup, select the new nozzle diameter and run the requested tests.
Do not continue if the nozzle is not fully seated, a cable is damaged or heating is unstable. The official CORE One nozzle guide provides the visual checks.
Nozzle wear is normally caught during routine checks, so the CORE One maintenance schedule is a good reference for spotting the signs before a replacement becomes urgent. If you are also deciding what to install next, a guide to nozzle sizes beyond 0.4 mm and the comparison between brass and hardened steel nozzles cover tradeoffs worth checking before ordering a replacement part.