Oxygen sensor replacement

1997 3.3
I need to replace the upper O2 sensor. Need advice wich way its easier, by the hood or from under the van.
Thanks

Never replaced one but I would bet it's easier from underneath though that's still a PITA. I would think you have to remove the wiper tray and or the intake manifold to get at it from above. I had one go a few years ago, took a look at the situation and headed to a local shop. Total $128. Based on that figure, they went from below.

Thanks for your answer.
Today I tried by removing the wiper tray and its np way to reach the sensor, then I tried by underneath, I can reach the sensor, put the special socket in the sensor with a ratchet but there is no room to work so I give up and I think I have to go to mechanic to do it, maybe I will try tomorrow again.

On my 96 I did it from underneath using the special socket borrowed from Autozone. There is little room but be patient and just do little turns at a time.