Add a Layer Mask and clean it up
Now that you’ve selected the part of your model that you want to use, go to your Layers panel
(Window>Layers) and click on the Add Layer Mask icon – it looks like a rectangle with a circle inside it. You’ll now just see the white selection, so now you have to hit Ctrl+I to invert your Layer Mask. Now you’ll see just your model and no white background. You need to tidy up your Layer Mask to make it look as realistic as possible. To do this, go to the Toolbox and grab the Brush Tool and choose a hard-edged brush. Set the Opacity and Flow to 100% and change the size with the [ and ] keys. Brush over any white edges that appear around your model or around the edge of your original selection.