Article V of the Constitution describes how to amend the Constitution. There are two ways.
Method I: First, 2/3 of the House of Representatives and the Senate must approve the amendment. Then, 3/4 of the states’ legislatures must approve the amendment.
Method II: 2/3 of the states call for a special convention to propose the amendment. Then, 3/4 of the states’ legislatures must approve the amendment. This method has never been used.