They make a special tool that is insterted between the window, gasket/seal (if present) and the trim
You can get by with a screw driver but if you mess up the moulding is bent and the surrounding paint will be damaged
Jeff Speegle
MCA Shelby Gold Card
http://www.geocities.com/MotorCity/6473
Mustang & Shelby research, documentation
http://albums.photopoint.com/j/View?u=1609818&a=12284202&p=44925357&Sequence=7&res=high.jpg