The founding fathers made sure the Constitution could adjust to changing times and attitudes by outlining an article that provided a method for amending the Constitution: Article V.
Article V of the U.S. Constitution provides two ways in which the U.S. Constitution can be amendment: the first one enables Congress to start the process, and the second enables state legislatures to originate it.
When Congress starts the process, both houses have to propose an amendment with at least two-thirds of votes in favor each. If the proposal reaches that majority of votes, then it is sent to the state legislatures or the state conventions to be voted on. Lastly, only if the amendment is approved by at least three-fourths of the state legislatures or the state convention, it becomes a law.
The second method enables state legislatures to propose a National Convention with two-thirds of votes. In the National Convention, the amendment can be officially proposed. Only if the amendment is ratified by three-fourths of the state legislatures (or conventions in three-fourths of the states), it becomes a law.