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At the bottom of one of the radiator side tanks is a drain petcock or tap. Loosen that off and drain off about a gallon or so of coolant.
To remove the belt...
Drive belts are equipped with a spring loaded automatic belt tensioner (Belt Tensioner). This belt tensioner will be used on all belt configurations, such as with or without power steering or air conditioning. For more information, refer to Automatic Belt Tensioner, proceeding in this group.