to take the frame apart, first the window must be taken off the bus.  Unscrew
the window latch and pull off the weather strip on the body of the bus.  This
will expose 5 small inset screws that must be removed.  This is usually a
real pain.   Be careful not  to mess up the screw heads or it'll be really
bad.  I like to use the screwdriver (reversable) that came in the original
tool kit.  

once the window is out, remove the weatherstrip on the outside of the frame.
 This will expose two pairs of two screws of the same type that held the
frame to the bus.   Care fully remove them and pull the two halves of the
frame apart.  

:)    easy as pie