I have a 97 ford ranger xl heater core bad . How do u replace it

I suggest you Google the answer. There is at least one good set of instructions with some pics at rangerstation.com, another at explorerforum.com. I found Googling several sources and using the Haynes manual together helped. It's easier than following the rather vague and useless Chilton/Haynes manuals alone. You have to pull the entire dash out, after removing air bags, steering wheel, steering column, all electrical connectors and THEN removing the heater assy to get at the heater core. It's a major pain and a big job, not for the faint-hearted. If you attempt it yourself, be sure to remove the negative. Battery cable, then the positive, then wait at least two minutes before starting, or you may get an airbag surprise. A former Ford mechanic told me they cheat and just cut out the heater core from the plastic box to save time. I'm choosing to NOT do this, since I don't have a 16 hour time limit imposed on me, and would rather leave everything intact, not butchered.