Well first of all, the Constitution can be interpreted in many different ways just like any other passage that you might read.These interpretations change over time based on events that happen and society changing.For example the Second Amendment has the possibility of being repealed in the near future because of public shootings.
An amendment is the only way to change the Constitution and they are formal as I'm pretty sure that both houses of Congress-the Senate and the House of Representatives- has to agree to the change.
