According to the declaration of independence, when should the people have the right to change their government?

The Declaration of Independence argues that people are "endowed by their Creator with certain unalienable Rights," and that the role of government is to protect those rights. When the government stops doing so, the people have a right to change their government. 

The Declaration is very specific about this: "To secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed."