To access all the spark plugs, I had to remove the air filter box and a part of the intake manifold, which was a bit tedious.
Afterward, I just had to disconnect the plug and could unscrew the spark plug using a spark plug socket.
I applied a bit of ceramic paste to each new spark plug and then reinstalled them with a torque wrench (in my case, 25Nm - check the manual if unsure). Connect the plug, and after 20 minutes, the job was done.
According to the manual, spark plugs should be replaced every 60.000 km.