O2 sensor 318i 91'

How do you replace an O2 sensor on a 91 318i? Thanks

not sure if the O2 sensor on the 4 cylinder is the same as the 6, but on mine it's located on the passenger side of the engine bay on the exhaust header. if i'm remembering correctly. pretty sure its just a pull/replace job, though might want to check a service manual briefly before proceeding.