Article Five outlines the process for the legal amending of the Constitution by both Congress (to the tune of 27 times) and the Constitutional Convention (to the tune of never... save for the original Constitution Drafting). Article Seven stipulates how the proposed constitution would become The Constitution.
At present, an amendment must pass both Houses of Congress with 2/3rds of the vote. It is then voted upon by the states until such time as 3/4ths of the states agree to the proposed amendment, at which time, it becomes a part of the constitution and enforceable as such. It has been common to put a time limit on amendments so that the 3/4ths of the state must make the change relatively soon. There is no hard rule for this, as the most recent amendment was passed by the States after Congress passed it with the original Bill of Rights.
The Constitutional Convention has never been tried and is therefor a bit of legal danger as there is no provision that supports the limited scope of a convention nor opposes it (One could call a Convention to pass a balanced budget amendment and emerge with a Constitution that makes North Korea look like a Democratic paradise by comparison, if not limited in scope.).
In addition, Article Seven is the article which describes the manner by which the Constitution would become The Constitution and what it needed to do to get there (get passed by 9 of the 13 states, at which time, the 9 undersigned states would be under the rule of the U.S. Constitution, while the remaining four would be left to their own device until they signed.).
An Amendment to the Constitution, is essentially a rewrite and there are several Amendments that overturn language in the Constitution (the 14th Amendment overturned the 3/5ths compromise in Article One, section 2, which at this time, only applied to penal servitude as slavery was outlawed in the 13th amendment). The 17th Amendment superseded Article 1, section 3 (originally states' legislatures appointed the Senators). The 18th Amendment was fully repealed by the 21st Amendment. When this happens, most copies of the constitution used for study will show this by having a line struck through the original text and further annotate what amendment affected this section to be struck out. It is essentially no different than you writing something down in ink, then scratching it out and writing a new item (this isn't done on original constitutions written by the framers... those are historical artifacts.).
Of course, there is nothing that allows the citizens of the United States to Rebel and form a new system of government that outright replaces the constitution. More importantly, to the framer's mind I suspect, there is nothing that says you Cannot Rebel and start your own new government (with Black-Jack and Hookers!) (Also, if you've read your Federalist Papers, they are much more candid that the Second Amendment was put there so the people had a way to rebel if it became necessary... one Federalist Paper openly states there should be no problem with a private citizen owning ships that were armed with cannons that could compete with contemporary naval vessels. Consider that the Founding Fathers were rebels). But by including the Amendment Process, they would hope to protect their rebellion from the next by allowing for ways to change the problems they did not think of in a less bloody method than their own rebellion.