The BEST way is with a hardware converter called a Terranex. Route the camera through that and capture. BlackMagic design makes them cheaper now, but still not cheap enough for many to buy. But many post houses have them in use.
Second Best....After Effects.
Third Best...something more at your disposal...Compressor. But you'll have to turn all the frame controls to BEST and then wait for a long time as it does this process. Unless footage is shot with 24p in mind (Cameras that shoot 24p Advanced, or some form of 24p), it will need some processing in order to make it look decent.