1st way:
An amendment is ratified after two-thirds of the House and Senate approve of the proposal and send it to the states for a vote. Then, three-fourths of the states must affirm the proposed Amendment. This is how the current 27 amendments were ratified.
2nd way for amendments to be ratified
This needs a Constitutional Convention to be called by two-thirds of the legislatures of the States. In the Convention, congress can propose as many amendments as it deems necessary. Those amendments then must be approved by three-fourths of the states.