B6

1.) In order for an amendment to be ratified, it must first be proposed. This can be done by Congress  having a 2/3 vote on it. After it is proposed it can then be ratified by  the State Legislatures where 3/4 of the states must vote on it.
2.) One informal method of changing the Constitution is judicial review. This gives the Supreme Court the power to interpret the Constitution anyway they want. Another method is through technology, over the years the use of more advanced technology has increased and has changed the constitution. Things like atomic warfare have increased the power that the executive branch can hold.
3.) Informal methods are used more often than formal amendment processes simply because it's quicker. It's easier to change with society than it is to go through the whole ratifying process, and the informal methods are not real amendments, just different interpretations.