The two methods prescribed by Article V
Every amendment to the US Constitution since the original 10 amendments in the Bill of Rights have been passed by the traditional method. It requires 2/3 of both houses of congress to approve the amendment followed by 3/4 of all states to ratify it.
A Convention to propose amendments to the United States Constitution, also called an Article V Convention, or Convention of States, may be called for by two-thirds (currently 34) of the state legislatures. It is one of only two processes authorized by Article Five of the United States Constitution whereby the Constitution, the nation's frame of government, may be altered.