2003 Mitsubishi Montero Error engine code P0155?

Hello i have my engine light on and autozone said its the Bank 2 Sensor 1, when i check under there are 2 sensor which one is is the bank 2 sensor 1?There is 1 at the top and 1 under, pls help me and i already buy parts which is Bosch 15600, pls tell me is this is the correct parts that need to replace the bank 2 sensor 1.Thanks