How to replace o2 sensor bank 1 sensor 1.

First, inspect the exhaust manifold. If there are any cracks present then you need to replace the manifold and gaskets, as well as the sensor. VERY common with Accents.

If the manifold has no cracks then continue on.

Run the car until it's at normal operating temperature then shut it off.

Using an o2 sensor socket and a ratchet with extension (all very cheap at auto parts stores) remove the o2 sensor. If it begins to turn hard on removal then stop and put it back in, you will need an exhaust manifold. You can take the plug off easy by using a flat head screwdriver to press the button that holds the plug together and wiggling the plug at the same time. Otherwise, put the new sensor in being careful to NOT TOUCH IT TO ANYTHING!

If the tip of the sensor contacts your skin, or anything else that has oils on it, the sensor will be rendered useless and you will have a check engine light.

Tighten the sensor down, plug it in. Drive to your local auto parts store and have them clear the code in the computer with their hand held scanner. This is usually free. If you did ok, you won't have a light come on and you will enjoy better gas mileage. If the light comes back on in a day or two then you messed something up or there was a crack in the manifold that you didn't catch.

Good luck!