In what way can American voters bring about changes in their
government?

#1: Voting. The right to vote was not passed for all for when people want change to hang around whining.
#2: Protesting. Unlike many countries, America is the one where you can peacefully protest whenever.
#3: Petition. If you want to show that people really don't like something and the people can't vote on it, the a petition is a great way to show that something needs to change.

Hope this helps!