How do I change the pre cat oxygen sensor?

I have 2003 1.6 petrol octavia.

I need to change the oxygen sensor on the exhaust manifold. (failed emissions and eliminated everything else)

However I can't get to it with any tools.

Has anyone done this - did you do it from above or below.

Did you take off the inlet manifold? If so how did you undo the bolts on the bracket underneath the manifold.

I am stuck on this and am hoping somone has experienced this before.

Thanks