loosen the main block bolt (which holds bottom of alternator to engine block, usually a 6mm allen key is used through a hole in the cambelt cover after removing a gromet), then loosen the bolt which connects to toothed bracket to the lifting eye hook (on 8v's similar on 16vs youll get the drift) then loosen the centre nut on the toothed locating/tensioning piece, every thing should then go slack, replace the belt, and repeat in reverse, push the alternator up with your hand until the gear engages with the toothed bracket, then use a spanner to wind it up the bracket till you get the correct tension on the belt, then whilst holding tighten the center bolt which goes through this to lock it, then tighten the bracket to lifting eye bolt then the alternator/engine block bolt and job done!!
all the above is provided the rack and pinion style sytem of tensioning the belt is working as often seized or rplaced for nut and bolt due to seizure, if its just nut and bolt then use a bar etc to hold alternator in position to get required belt tension then tighten the nut/bot to lock it...
easy!
