2002 Ford Taurus oxygen sensors

Have message on computer about bank 1 sensor 1 on my vehicle. Which bank of the engine is this sensor on and its exact location please. Also how difficult is it to change this sensor. I have notice that if the sensor is on the back bank of this engine (next to the firewall) that I may possible have to remove the intake manifold to change out the sensor it the sensor is on top of the exhaust manifold on this bank. Thank You for your Help.

J Bundridge