The world is not overpopulated; the average human lives a far better lifestyle today than at any time in the past, despite the fact that there are 7 billion of us now. This is because technology has improved much, much faster than population has increased...and there is good reason to believe that this trend will continue into the foreseeable future.
With that said, there are certain PARTS of the world that are overpopulated...Sub-Saharan Africa and (especially) South Asia. Draconian approaches like setting birth limits will not work, as China has demonstrated. Birth limits will lead to grotesque gender imbalances, human trafficking, and social instability. A better approach would be to help poorer countries improve their standard of living. Birth rates tend to decline as people become richer, because children become a financial liability rather than a financial asset.