So it depends on the schools you are applying to. The schools I want to apply to mentioned to me that it is the upward trend and prerequisite gpa that they care about most. They suggested that I retake my C's for A's. It is not frowned upon, it makes you look better because you are determined to be admitted. I retook gen chem II at my local community college and received an A. I am only applying to schools that replace the old grade with the new, so this benefited me.