This is that change that would really make a difference in the entire political structure of the US. If there are four candidates for president, you number them in order of preference, voting only for the ones that you actually can support. You don't vote for anyone you can't support.
In our current situation this would play out in interesting ways, considering how unpopular both Trump and Clinton are. If everyone knew that they could vote for their first choice, and if that person did not get a majority their second choice would get their vote, they would feel safer in voting for "third" party candidates. As it is we will almost all vote for "the lesser evil" because we despise/fear the other one so much that we'll stomach our choice. This maintains the two party system in which both parties are corrupted by the involvement of big business.
I wouldn't mind either if we were to trend toward the British style system with a parliament. We don't have to ditch our constitution in favor of parliamentary acts, we don't even have to call it a parliament, because it is analogous to our congress. The beneficial change would come from allowing coalitions among major and minor parties to form in order to win, which then brings fresh faces and ideas into congress. It seems obvious to me that we need to broaden the sphere of public life to include more than just two sets of talking points that don't even speak the same language.
I know that no such radical changes are on the horizon. Our nation and our congress are so drastically polarized that compromise or consensus seems out of the question. But eventually this page will turn. I look forward to a shift in our culture, and to the possibility that we could improve our system to reduce corruption and increase our ability to adapt to fast-changing times.