It's not a problem and won't be, on a global scale. Overpopulation is only a problem in places that don't have sufficient infrastructure to sustain the population in a crisis or the scientific advancements to remedy such issues like more developed counries do.
Doomsayers like to point at famines in highly populated, desert climate, poorly developed countries like Ethiopia and say 'that's what will happen to the world eventually'. No it won't. Agricultural techniques are already so advanced the amount of food you can grow regardless of space or climate is staggering. Just need to have the infrastructure to apply them.
More advanced tech will spread, poor places where lots of babies are born will become more wealthy and the population growth will start leveling off, then decline and settle at a lower number when the large cluster of elderly die. It's the natural proces of a country when the economy transitions to a developed one. It's happened in all developed countries, it's happening in China right now, it's gonna happen in Nigeria too.