Can i retake a core class?

I've already graduated with my Bachelors and I'm applying to grad school. I didn't realize till now how important some of those classes in undergrad were. Is there a way to retake like 2 classes before I apply to grad school and get rid of my C's..? or is it too late to fix it now? I don't really care if it affects my overall gpa or not.. I just want a better grade on those 2 classes.