Coolant for 1994 4.0 Ranger xlt
 

I would like to know how I go about flushing the radiator on 1994 ranger. I'm not sure what kind of coolant the last owner had in it since it looks like brownish sludge in the reservoir? The owners maual says to use premium cooling system fluid that meets ford specs ESE-M97B44-A. The previous owner said they flushed the radiator but didn't mention when or what they used. Please help. Thanks