If you did poorly in a prerequisite, you should take it again. There are stories of success with poor grades on their transcripts (I know a successful ER doc who told me he got a D in Orgo), but these people are rare. My advice is to take this course again.
If the course is not a pre-req and some time has elapsed, leave it be. You prove your mettle by acing your pre-reqs and demonstrating success in the nearer term. I had some poor non pre-req grades on my undergrad transcript from freshman year. When I applied to medical school at age 35 it didn't seem to matter.