What major change did Constantine bring to Byzantium?

Constantine the Great was the Roman emperor from 306 to 337. From 324 he ruled as sole ruler.

Constantine's rise to power took place in the context of the dissolution of the Roman tetrarchy, which Emperor Diocletian had established. In 306, Constantine inherited his father Constantius I after his soldiers had proclaimed him emperor. By 312 Constantine had prevailed in the west, 324 also in the entire empire. His reign was particularly important because during his term Christianity's rise to become the most important religion in the Roman Empire began. Since 313, the Milan Edict guaranteed freedom of religion throughout the empire. Subsequently, Constantine privileged Christianity, paving the way for it to become the official religion of the Empire. Inside, Constantine pushed ahead with several reforms that shaped the empire during the late antiquity. In terms of foreign policy, he succeeded in securing and stabilizing the borders.

Answer: By putting christianity into the full of rome including byzantium.