§1. It is for the Roman Pontiff alone to convoke an ecumenical council, preside over it personally or through others, transfer, suspend, or dissolve a council, and to approve its decrees.
§2. It is for the Roman Pontiff to determine the matters to be treated in a council and establish the order to be observed in a council. To the questions proposed by the Roman Pontiff, the council fathers can add others which are to be approved by the Roman Pontiff.
Source: Code of Canon Law (Vatican.va)