Hi 
I've added Lady Di's figure, from the last exercise, as I'm not very photogenic 
 
 
 
 
Start Image (Archbishop) > Duplicate Image
Select Second Image (Lady Di's) > Select Move Tool from tool box > Move cursor over it, Press down mouse button, and drag onto first image > resize using Free Transformation tool (under Edit) to get head to similar size of Arch. > Drag top layer down below Duplicate layer in the Layer palette (ie between Duplicate and  Background layers)
Select Duplicate layer and use rubber tool to rub out the Arch.'s face 
Tidy up using clone tool and smoothing tool, and do final adjustments using move and transformation tools
Mudge