How do you replace a heater core in a 2004 chevy cavalier?

my husband is going to do a side job and would like to have step by step instructions on how to do this....please no rude comments thank you for your help.How do you replace a heater core in a 2004 chevy cavalier?There may be instructions on www.ehow.com, or in the Chilton repair manual that can be viewed at a library................I would question the heater core being bad on a vehicle that's only 7 years old - they usually last many years before needing replacement................maybe it's another problem like the thermostat that need replacement ???