Vectra mk2, replacing the alternator

Hi all,

My alternator died so will need to replace it soon as currently I am running with 3 batteries recharging and swapping them around if required.

What is the best way to replace the alternator?
Referring to the Haynes I have to remove
the right wheel and some plastic liners,
the air box and intake elements up to the throttle body,
remove the coolant hose from the engine block,
remove some other stuff which I can't find,
what I find is the ECU above the alternator.
This is on the right side of the throttle body on the photo in the Haynes manual. But actually it on the left side of the throttle body in my car, almost above the alternator.
I am a bit scared to touch the ECU but it seems no other way.
Not to mention I have concerns about how to release the tensioner once I put the new alternator on.

Any of you guys have an idea what is the easiest way to replace the alternator?