Oh and your car doesn't have a fan belt. It's the alternator belt... ;)

^^
then tighten

Lever the alternator back with a breakers bar ;)

rocky, if its 1.2 8v as it says in your gallery mate, its really easy, did it on mine about a month ago, basically where the alternator is, there is one bolt holding it to a bracket attached to the side of the engine block. Undo the bolt at the top of the alternator, push the alternator as far back as possible (probably best to lever it back to get it as tight as you can), thrn do it as best as u can. Then try to move the belt, the middle of it between the two pulleys should move about 8 to 10mm from its rest position. Hope this helps you mate!

It's not a fault. It's because the belt hasn't been tightened.

I been told this is a commen fault with corsa b's anyways when i rev engine first thing in morning the fan belt starts squeeling like hell in other words either moisture or cold on fan belt is there anyway to stop this cause its doing my nut in when i go around corners or at stand still at traffic lights squeeling noise and everybody looking at me :|