The alternator is probably held on by three bolts. Firstly have a good look at where the existing belt is fitted and how many pulleys it runs. Loosen the three bolts and gently move the alternator inwards to loosen the belt. Take belt off. Replace belt and push alternator back out, you might need to wedge it with something to keep it in position. Tighten the three bolts. Job done. Remember to remove wedge if you have used one!
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