Why was the constitution changed?

" The Eighteenth Amendment to the Constitution had ushered in a period of time known as "Prohibition", during which the manufacture, distribution, and sale of Alcoholic Beverages was illegal. Passage of the Eighteenth Amendment in 1919 was the crowning achievement of the temperance movement, but it soon proved highly unpopular. Crime rates soared under Prohibition as gangsters made millions of dollars on illegal alcohol sales, and corruption was rife among law enforcement agencies." - Wikipedia

Summing it all up, the Eighteenth Amendment of the Constitution was repealed (by the Twenty First Amendment) due to the increased crimes of production and transportation of liquor throughout the United States.

Numerous liquor dealers were incarcerated, respected citizens neglected the mandate of Prohibition and public opinion opposed the law.