How to replace the spark plugs?

Yep, first you need to remove the engine cover. I would do the job with the engine warm but not hot, also, use a spark plug socket because it has a rubber insert to protect the plug from cracking. Here is the part numbers for the spark plugs and the torque to tighten them down too, don't worry about the gap because it is set at the factory.

NGK Laser Iridium - Part No. ILZKR7B11 (Honda P/N: 12290-R70-A01)

13 lbf ft (17 Nm) on a clean, dry thread

Check out the images (below). Let us know if you need anything else.