There are as always many ways to do it. For example using channels but this time we will try to do the job using the Background Eraser tool. This works well for a background that is contiguous.
Set your settings to this.
The tolerance is depending on your image so try and see what works best. Click on the hair to set 'the protect Foreground colour'.
Now we can paint over the background to erase it.
Just try it out and if you done it you can easily change the background.