It's more important for humans to survive than another race. Don't always think about others, and think about yourself. Be an Objectivist, or at least rational self-interest. You have to protect yourself first, and then others second. It's nature. If the intelligent life cannot protect themselves, another one will take its place.
I believe if Earth was dying and we found another habitable world we should definitely move there because we are unique and complex species ourselves an it would be pity and a great tragedy for humans to disappear. HOWEVER the word "occupy" sounds a bit violent and unsuitable I think. There is no need to "occupy" another world by force. I believe it would be much better and wiser to try our best to cohabit with those intelligent species and learn more about each other and about our universe.
For us to sacrifice another race so that ours may survive would make us no better than the hostile aliens we see in popular culture. If humans want to present themselves as knowing right from wrong, then show it. We must be respectful of all lifeforms we encounter. We can coexist.