The Founders knew there were unresolved issues (slavery in particular) and others they couldn’t foresee, so Article V of the Constitution makes it possible to amend, or change, our Constitution. There are two methods, neither of which involve either the Executive or Judicial Branches. Both rely heavily on the states.
So far, there have been 27 amendments, all of which started in Congress. The first ten are the Bill of Rights and two states refused to ratify the Constitution without the promise that a Bill of Rights would be passed quickly and sent to the states for ratification. Twelve amendments were passed by that first Congress. Ten of them went on to be the Bill of Rights, one was never ratified, and one finally became the 27th Amendment in 1992.
Under that method, Congress must first pass an amendment with a vote of two thirds in favor. It is then sent to the states for ratification. When, and if, three fourths of the states required it, it becomes part of the Constitution. That means that while it only required ten states to ratify what became the 27th Amendment when it left Congress, it required thirty eight by the time it finally became part of the Constitution in 1992. Amendments that pass Congress are not guaranteed to become part of our Constitution. Not all receive enough ratifications to become part of our Constitution.
In the 20th century, many (but not all) started to have deadlines for ratification. The Equal Rights Amendment (ERA) had a seven, extended to ten, year deadline for ratification. After ten years, thirty five of the required thirty eight states had ratified it. The ERA is one of six amendments passed by Congress that failed to become part of our Constitution.
There is a second way to amend it. That is for the legislatures of two thirds of the states, currently 34, to send Congress a request for a Constitutional Convention. Other names for it are a Title V Convention (the Constitutional basis for the convention) or Con Con. Any amendments they pass will still need to be ratified by three fourths of the states. To date, this has not happened, but there are standing requests from 32 states to have a Con Con. That means we only need requests from two more states and it will happen. In this method, the Legislative Branch (Congress) joins the other two branches in playing essentially no role in crafting or passing the amendments. They actually call the Convention, but it is not their choice and they have no involvement beyond this. The states control the process from beginning to end.