Maybe @Antman won't mind me adding here for the later models (2013+ I think) that have the air switching valves in the way of a few of the plugs. I wouldn't think there are too many folks that have many miles yet, but at some point it will come into play. With a 2016, I obviously haven't done this, so it's just pics of the interferences you'll have to remove. Sorry, I don't have the panache of Miss Gracie. You'll just have to bear with me on a boring writeup.

So this is an air switching valve that blocks access to a couple of the plugs. There is one on each side of the engine. They are not identically shaped due to mounting point differences, but other than that they are the same. The one shown in the picture is on the passenger side.



To remove the air switching valve:
1) First remove the attached air tube by removing the 4 bolts/nuts (yellow circles), 10mm socket. At each end of the air tube, there is a metal gasket. The gaskets will be replaced but be sure not mar the mating surfaces.
2) Disconnect the electrical connector and rubber hose from the valve (blue arrows). The rubber hose is attached with a standard spring clamp. Pinch the two tabs together with a pair of channel locks to widen the clamp for removal. Make sure you take note (or pic) of how the hose and clamp were aligned. There is a paint mark on the hose that lines up with a raised projection on the valve body. You will want the hose and clamp lined up properly when you reinstall.
3) Now you can remove the 3 mounting nuts (red circles), 12mm socket, and then remove the valve. The 2 that are visible are easy to get to. The one you can't see in the picture is behind that wiring harness. This nut may be the one thing that could complicate this job, so I'll focus on it for a second.

The FSM actually has you remove the air cleaner cap and hose before you mess with the air switching valves. The only reason I can see you would need to do this is for that one mounting nut on the passenger side air switching valve. So I recommend assessing this and trying to loosen that nut before starting this job. If you think you need to, go ahead and remove the air cleaner cap and hose before you start on the air switching valves. Here's how you would do that.

In the picture below
1) Unfasten the 4 hook clamps (red circles), just like your were replacing the air filter.
2) Disconnect the mass air flow connector (yellow circle)



In the picture below
1) Remove the rubber vacuum hose and detach the wiring harness (red arrows)
2) Remove the mounting bolt (yellow circle), 10mm socket
3) Sorry the next two are not pictured cos I was too lazy to take the engine cover off, but it should be obvious with it off
4) Remove the rubber ventilation hose, has a spring style clamp just like the hose on the air switching valve
5) Loosen the screw-style clamp on the hose where it attaches to the throttle body
6) At this point (unless I missed something) everything should be disconnected and you can wiggle and lift the air cleaner assembly out and set aside



With air cleaner cap and hose off, you should have no problem accessing all the mounting nuts and removing the passenger side air switching valve. For the driver side, it's basically the same except you don't have the air box in the way. After removing both air switching valves, you should be set up to do the spark plug replacement just like shown in the OP.

Installation of everything is essentially the reverse of removal. Just remember to get everything lined back up the same way. And also you're dealing with engine intake that is taking in air that goes through your filter so you do not want any foreign material getting in all that stuff during removal or installation, so keep it clean. Here's the torque specs for all the extra stuff and part #'s for the air tube gaskets, etc. that you'll need. I'll also point out that depending on your model year, the spark plug part # is different, so check that below as well.

Torques:
Air switching valve mtg nuts - 186 lb-in/21Nm (12mm)
Air tubes - 88 lb-in/10Nm (10mm)
Air filter hose clamp - 44 lb-in/5Nm (10mm)
Air filter hose mtg bolt - 44lb-in/5Nm (10mm)

Parts:
6 spark plugs
Toyota part # 90919-01233/DENSO SK16HR11 ('14-'16) or
Toyota part # 90919-01191/DENSO SK20HR11 ('10-'13)
4 gaskets for air tubes - Toyota part # 17377-38010


Hope this helps. First time doing something like this and I'm sure I messed something up or missed something. Certainly willing to take some feedback to make it better.