It'll be clearly noted in the product description whether your pod kit takes replacement coils or pods. Either way, you'll know your pod or coil needs changing once your E-Liquid starts to taste burnt.
At this point, if your pod kit uses replaceable coils, simply replace the coil inside the pod. And if your pod kit uses pods with built-in coils, you should instead replace the entire pod.
If you're buying a new pod kit and are unsure what type of replacement pod/coil your kit needs, please read the product description. If you already own a pod kit, we recommend referring to your manual.