It really depends on why you got a C in it. Did you struggle with the material, or did you understand it and just make mistakes regarding exams and/or homework? Was there one exam that really killed you, even though you did alright on the others?
Some higher-level math classes take for granted that you know how to integrate if necessary. As Steff196 said, you'll probably never have to know the integral of (1/x^2)(1/sqrt(1-x^-2)) off the top of your head again, and if it does come up, you'll probably be able to look it up. But you do need to have an intuition of what an integral is, and how to construct one if given a word problem.
Similarly, with infinite series, it's definitely good if you know how to expand a function into a series, but the most important thing is your understanding of the underlying concept. Do you see why you can write things as series and when they serve as good approximations, do you know the basic form of a power series, do you understand at least the principles behind convergence, and does it make sense why/how you can shift, differentiate, and integrate them? If you have all that down, it's fairly simple to relearn convergence tests or re-memorize a particular function's series. If you didn't gain that intuition in calc 2, however, some more advanced versions of infinite series (series solutions to differential equations, Fourier analysis, etc.) might give you trouble.