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

Governments are created BY the people FOR the people, according to the Declaration of Independence. When a government fails to serve its people, the people have the right to change it.

"That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, — That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness." 

This basically states that when a government abuses its power over its people, it no longer has the right to rule, and the people have the right to establish a new government that will keep them safe and ensure their happiness.