How did bipedalism in humans support the evolution of our skulls?

We could do thing with our hands without having to use some of our energy in getting up to try to balance on our two rear legs.

The evolution of human bipedalism which began in primates about four million years ago or as early as seven million years ago with sahelanthropus has led to morphological alterations to the human skeleton including changes to the arrangement and size of the bones of the foot, hip size and shape, knee size, leg length, and the shape and orientation of the vertebral column. The evolutionary factors that produced these changes have been the subject of several theories.