1989 royale heater core?

Hi everybody .. I'm pretty new here and hope you can help with some tips for me on replacing my heater core?? When I turn on my defroster the windows fog right up and won't clear and yes.. I can detect a slight smell of anti freeze in the veh. I've never performed this repair before. I have a bit of an idea how to do it.. but am just looking for good tips or if someone has a link of where i can go for a step by step would really be helpful

thank you in advance!