Put plastic under the gasoline and oil caps and tighten them up to prevent spillage.
Tip the lawn mower on its side and wear heavy-duty gloves to prevent accidental cut on your hands when removing the blade.
Using a wrench turn the bolt that is securing the blade counter-clockwise until the bolt comes out.
Now, either you just want to sharpen the blade or change it for a new one, that’s your decision.
A new blade will somehow produce a cleaner cut because it still balanced and factory sharpened.