Did you get a manual with the deck? The simple instructions are in there. But seeing as how you're asking the question, with any mower you need to block (piece of wood) the blades from spinning when you attach the ratchet wrench to the blade nut/bolt.
You may need a "breaker bar" which can be a short length of pipe slipped over the ratchet handle to help break the nut/bolt. OR...get a hold of an impact driver. Air/battery/electric powered...all will make the job very simple. Just get the correct size socket and zip that nut/bolt off in the wink of an eye...no other doodads needed.