Article V of the United States Constitution

Article Five of the United States Constitution describes the process whereby the Constitution, the nation's frame of government, may be altered. Altering the Constitution consists of proposing an amendment or amendments and subsequent ratification. Amendments may be proposed either by the Congress with a two-thirds vote in both the House of Representatives and the Senate or by a convention of states called for by two-thirds of the state legislatures. To become part of the Constitution, an amendment must be ratified by either—as determined by Congress—the legislatures of three-quarters of the states or state ratifying conventions in three-quarters of the states. The vote of each state (to either ratify or reject a proposed amendment) carries equal weight, regardless of a state's population or length of time in the Union.

Additionally, Article V temporarily shielded certain clauses in Article I from being amended. The first clause in Section 9, which prevented Congress from passing any law that would restrict the importation of slaves prior to 1808, and the fourth clause in that same section, a declaration that direct taxes must be apportioned according to state populations, were explicitly shielded from Constitutional amendment prior to 1808. It also shields the first clause of Article I, Section 3, which provides for equal representation of the states in the Senate, from being amended, though not absolutely.

...
Wikipedia