corsa c 2002 lambda sensor?

I have engine light on my corsa,the code is 0141 o2 heater sensor bank1 sensor 2, the car is working ok but emmissions have goone up, i believe ther are 2 sensors, 1 up in the manifold and one directly below the engine in the exhaust pipe. which sensor is bank 1 sensor 2? and will changing the sensor be the first thing to do.