Hi newbie question here

I wanna change the o2 sensors after scanning a check engine light but have no clue where they're located.
so far as part numbers i have;

Bosh 1340
Bosh 13642
Bosh 13862

I wanna replace them all while at it.

Thanks

 

They are located downstream from the Exhaust Manifolds.
The sensors are before and after the primary catalytic converters.