post a detailed description on how to replace an 02 sensor off a 98 ssei? or do i need to take it somewhere or will napa do it for me?

its not very hard. i jacked up the car a little and did it from underneath. mine came out easy. you want the proper size wrench. an adjustable wrench might slip if its tight. on a difficulty scale of 1-10 its a 2.

It'* the spark plug looking thingy in your rear exhaust manifold. Sticking out the top. Ignore the one after the catalytic converter. It has no effect on performance.

Lefty-loosy, righty-tighty.