I'm assuming you're asking how to go about retaking them at your undergrad and not so much about how to report them on an application?
It's going to vary depending on the university/college but it could be as easy as just signing up for that class again when you register. If it won't just let you register that way you may have to go to that specific department, meet with an advisor who can then sign you up for that class.
I retook one or two classes and it had been several years since I originally took them and since then the course numbers and some other features changed so I had to the department to get permission to retake a similar course.