change the one right under the hood facing forward.

This one is very easy to get to. It is the air/gas mix sensor affacts perfomance. ( My experience, this one goes first. Even if you are wrong, it will need to be replaced soon anyway . The other one is under the car on the exaust pipe---hard to get to).You need a soket with a slot. Parts store will know. Autozone will even let you borrow one. After replace this sensor, use a code reader erase the code. ( if you buy your part at autozone, they might erase it for you...)
Hope this helps.
I once fixed one of mine this way.