How can the US Constitution be amended?

There are two ways, one of which has never been done. That one is for Congress to call for a Constitutional Convention. They would have to pass several laws governing the nature and specifics of such a Convention.

The other way, the only one that has been used to date, is for Congress to pass an Amendment by 2/3 vote of both chambers and then submit it to the States for ratification. 3/4 of the States’ legislatures would have to approve it to pass.