Whether they do or not, PharmCAS will take both grades and put it in your calculated GPAs. Still, I think retaking something for a higher grade shows more effort and reflects better on your part than leaving it as a C for a one time take when you list both grades on a prereq sheet. And if you received lower than a C, likely you would have to retake it regardless.
To OP, you should be able to retake just the one part of the sequence, not the whole sequence unless the school you want to take it at has any odd rules about that..