2002 OBDII code PO155 Heated Oxygen Sensor

You did not tell us what make or model you have? Most front drives, it's the sensor on the front side of the engine. The first one you come to at exhaust manifold to the converter.

bank 2 means on the passenger side. follow your exhaust pipe towards the front of the vehicle. you will need a small flat head screw driver to remove the clip and an adjustible wrench or an open end box wrench(recommended) to unscrew the sensor from the exhaust pipe. at a auto parts store tell them you need the O2 sensor for 2-1. not all sensors have the same length for the wiring. the sensor looks like a 8 inch long spark plug with wires attached to the back. remove clip, unscrew sensor, replacement is reverse.