Doesn't have to come out.
You first need to remove the instrument panel. After you remove that then you need to remove the Plenum Assembly. Drain the coolant from the system then disconnect and plug the hoses going to the heater core.
This is not an easy task and should not be attempted unless you are very skilled and very familar with working on vehicles. This is typically an 8+ hour job for a mechanic/technician and involves your air bag system.
1995 and later models are done in this order, disconnect the negative battery cable, remove the instrument panel, remove the evaporator core housing, drain the radiator, disconnect the heater hoses, remove the nuts and the plenum chamber, remove the screws and remove the heater core cover, remove the heater core. Installation is reverse of removal. Sounds easy but it can be a lot of work but it is a lot easy than pulling your entire dash. Don't forget to reservice your radiator fluid and havew your air conditioner reservice. You'll save a lot of money following these procedures. Good Luck!