Honda 250 O2 Sensor location?

2016 Honda 250 HP
I pulled the codes and it says it is the O2 sensor.
Where is it located?
What tools do I need to change it?
Is this something I can change myself?

I found a parts diagram. The O2 sensor in the diagram is #14.
Not sure exactly where it is. I assume it is on the port side of the engine toward the back up high.
I hope it is not buried deep inside.

If it's the same as the 225, it's on the port side exhaust manifold, almost halfway down and easy to get to. Don't confuse it with the manifold temp sensor, which sits on top of the exhaust manifold.

Let me try to upload a diagram here: View attachment HO2 sensor removal.pdf

SOLVED!
I was confused, because when I put in the motor's serial number on the Honda Marine site it came up with two different numbers for the O2 sensor.
Just the O2 Sensor was $249, but the O2 Sensor Assembly was only $60 and it said it included the clip and sensor???
So I decided to run be the local Honda Marine dealer.
They looked it up and the same thing. They too were confused.
I was looking at their monitor when they pulled it up and I saw the original invoice come up. I noticed it said the warranty expired in 2019.
BUT! I looked a few lines down and it said emissions warranty valid thru 08/06/2020.
I pointed it out to them. They got on the phone and sure enough, it is under warranty. They extended the emissions warranty because of problems with the O2 Sensor.
They said they will call me when the part comes in and I can bring the boat by and they will change it out quick while I wait.
So Happy!

BTY, the $60 assembly was a price drop to make it affordable to replace the original O2 sensor, which was aparrently faulty.

Well that's darned good news! Did they hook up Dr. H to confirm that the HO2 sensor had failed? If not, ask them to do that to confirm that's the problem.