Access one of the selection tools, e.g. Selection brush tool or Lasso tool, and make a selection of the head. When the selection is complete, you will see "marching ants" surrounding it.
Go to Layer>new>layer via copy. This places just the head on its own layer.
I assume that you want to place the head on a new background. To do that, go to Select>all, then Edit>copy. Open your new background, go to Edit>paste. Move the head using the move tool and resize with the corner handles of the bounding box.