I'm not quite sure exactly what your question is, since Hercules is Heracles. Perhaps you are asking why the name Hercules is more commonly used? It is because the transmission of Greek mythology through Antiquity, the Middle Ages, and into the Renaissance was almost entirely in Latin even when drawing on Greek sources. This largely established the usage of Hercules rather than Heracles for this figure.

If that's not what you're asking, feel free to clarify.