We will have to build bigger cities in what we consider unhospitable places, like in the desert, under the sea or floating on the sea, that would take care of the where to put people situation, we would then have to find a better source of energy something clean like solar or wind power on a bigger scale than we do now.
Feeding the population would need to be by using genetically modified crops that could grow say in the desert.
We could move into space either on another planet or on huge cities floating above the earth, failing that we could all just kill and eat our neighbours, there are lots of viable solutions.

Cheers

NCM