who has the power to amend the constitution and how often does it happen?

Answer 1

Congress. Doesn't happen all that often.

Answer 2

The power to amend the constitution is spelled out in a particular country's Fundamental Law or its Constitution. For example, in the Philippines where I am a Citizen, the Constitution states that our Consititution may be amended by the people at large through a process called people's initiative; by the Congress sitting as a Consitutuent Assembly; and, finally, by a Constitutional Convention whose members are elected by the people with the sole task of amending the Constitution

Answer 3

It requires a 2/3 majority in Congress, then it has to be ratified by 2/3 (edit: oops, it's actually 3/4, 2/3 of the states can bring up a constitutional amendment or 2/3 of Congress can) of the states to become part of the Constitution. It has only happened 27 times.

Answer 4

A Constitutional Amendment must get through the House of Representatives and Senate. Then it must be ratified by a plurality (2/3, rather than a simple majority) of the 50 U.S. states. I does not happen often because it isn't easy, which is what the framers intended.

Answer 5

In short 'The People' who are "sovereigns without subjects" hold the power to amend the (or even create a new) Constitution. I can't recall the quote at the moment that refers to creating a new form of government,

The last amendment known as the 27th was ratified in 1992.
The amendment known as the 26th was ratified in 1971.

The following is from the source site listed below:
There are essentially two ways spelled out in the Constitution for how to propose an amendment. One has never been used.

The first method is for a bill to pass both houses of the legislature, by a two-thirds majority in each. Once the bill has passed both houses, it goes on to the states. This is the route taken by all current amendments. Because of some long outstanding amendments, such as the 27th, Congress will normally put a time limit (typically seven years) for the bill to be approved as an amendment (for example, see the 21st and 22nd).

The second method prescribed is for a Constitutional Convention to be called by two-thirds of the legislatures of the States, and for that Convention to propose one or more amendments. These amendments are then sent to the states to be approved by three-fourths of the legislatures or conventions. This route has never been taken, and there is discussion in political science circles about just how such a convention would be convened, and what kind of changes it would bring about.

Regardless of which of the two proposal routes is taken, the amendment must be ratified, or approved, by three-fourths of states. There are two ways to do this, too. The text of the amendment may specify whether the bill must be passed by the state legislatures or by a state convention. See the Ratification Convention Page for a discussion of the make up of a convention. Amendments are sent to the legislatures of the states by default. Only one amendment, the 21st, specified a convention. In any case, passage by the legislature or convention is by simple majority.

The Constitution, then, spells out four paths for an amendment:
Proposal by convention of states, ratification by state conventions (never used)
Proposal by convention of states, ratification by state legislatures (never used)
Proposal by Congress, ratification by state conventions (used once)
Proposal by Congress, ratification by state legislatures (used all other times)

It is interesting to note that at no point does the President have a role in the formal amendment process (though he would be free to make his opinion known). He cannot veto an amendment proposal, nor a ratification. This point is clear in Article 5, and was reaffirmed by the Supreme Court in Hollingsworth v Virginia (3 USC 378 [1798]):

Answer 6

The US Constitution can only be ammended during a Constitutional Convention. Congress has the power to call a Constitutional Convention but it takes a two-thirds majority of both houses to do so.

Answer 7

To contradict what a couple of people above have said:

Amendments can be proposed by a vote of 2/3s of both chambers of Congress or they can be proposed by a convention called for by 2/3s of the states. But in order to be ratified and to take effect, it takes 3/4s of the states, not 2/3s of them. States can ratify either in the state legislature or at state conventions.

Answer 8

Congress has the right and if I remeber correctly it takes a 2/3 majority in both houses, it rarely happens.