You want to challenge paramedic, but your bio says your an EMT-Basic. In order to challenge something, you have to have skills and knowledge at least equivalent to what you are challenging. Most people challenge paramedic from being a RN. If you are already a paramedic, you need to make sure you have what NYC needs for reciprocity. If you're an EMT-Basic, you need to take an accredited, full-length paramedic course in order to become one.
BTW Most places don't call their courses a challenge refresher as no where that I have heard of has a course specifically to challenge an exam. Look for paramedic refresher courses intended to teach re-cert for national registry.