Code P0154, where is the Oxygen Sensor located?

Yep, the primary oxygen sensor is up near the engine's exhaust manifolds while the secondary sensor is down on the exhaust system after the catalytic converter. Here is a generic guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

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

So, the sensor is located underneath the car correct I can't do it from the hood?

You can change it from under the hood. Bank 2 sensor 1 is near the cylinder head in the exhaust manifold on the left side of the engine closet to the radiator.