One other thing to note if your changing the alternator belt is to also change the idler pulley at the same time.
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The bearing is held in the pulley with an internal circlip. So circlip pliers are advised for ease.
The bearing might need a tap with a hammer to get out. You can use a suitable socket for this. When fitting the new one, make sure the socket fits on the outside of the bearing and not the inner and tap it in. You can clean the pulleys with sandpaper to get rid of any rubber deposits and ensure a good grip on the belt.
When tensioning the belt leave the 12mm nut finger tight and tension the belt. Your looking for 1/2 INCH approximate travel on the belt on its longest run, which is the bottom one. Never over tension the belt. Then tighten the 14mm nut to lock into place. Turn the alternator to make sure its not slipping. Before putting all the inside back together give it a run and rev to make sure its not making any unwanted noises.