Your mower manual will tell you exactly how to remove and replace (or change) the blade. You put a screwdriver, or something equivalent, into a small hole to stop the blade from turning while loosening the nut. Yes, turn the nut CCW to remove it (Lefty Loosey). Note that it is torqued to around 40 ft lbs so you'll need a long-ish wrench, or torque wrench, to break it loose. Also, the torque wrench is handy when tightening the nut back to the 40 ft lbs after the blade is replaced. There is a washer that needs to go back on in the same place it came off so pay attention to that. Also, the blade has to be installed with the "this side toward the lawn" stamped on the blade facing the lawn when the mower is in its operating position. Double check the manual. It's really an easy job, just need to make sure you can loosen the nut and properly tighten it.