I'm replacing the alternator and i need to loosed the belt do I loosen the nut in the center of the pulley and then use the adjuster to loosen the belts?

 

Yes, loosen the nut slightly on the idler pulley and then use the adjustment to take the tension off the belt. You may want to spray the adjustment bolt liberally with WD-40 or equivalent if there is any corrosion present. It's a PITA if it snaps.

 

Thanks for the help.