Depends on the school. They usually mention it somewhere on their admissions requirements on their school website. I've had to email them and ask before though.
If they are a PTCAS school, then the retakes are averaged. Now they can do their own calculations, but you generally would have to be above the cutoff GPA.
Some non PTCAS schools do replace courses. You just have to contact the schools you're interested in and see what their policies are.