according to Jefferson whendo people have right to alter or abolish a government?

Answer 1

From the Declaration of Independence:

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — 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..."

Thus, the people may alter or abolish a goverment whenever it fails to secure the rights to Life, Liberty, and the Pursuit of Happiness, or it infringes upon those rights.

Answer 2

"People have the right to dissolve their government, if that government ceases to work solely in their best interest."

This is a quote from near the bottom of the third paragraph. Hope this helps!