Where will people migrate when the planet becomes too populated?

Although some people will say people will migrate to another planet when Earth becomes overpopulated, I will say that people should stop having so many children. If we don’t do something to save this planet, what’s to stop us from wrecking the next place?
In reality, it’s not that we, as humans, are leaving too big a footprint as we stomp the Earth down, drive species into extinction and destroy the environment. We can live like kings and queens, enjoying all the great benefits of modern life. The problem is that we are already overpopulated. Couples need to restrict the number of their children to two or less. Sadly, though, that will never happen.