Lay a razor knife against the glass so the tip goes under the seal and start cutting, careful you don't go so deep you scratch the paint on the frame, once a little is up you can usually rip the old seal's outer 1/2 off leaving the winshield ready to push out into your helpers waiting hands. Don't be shocked if you need to do some paint and possibly some rust work under the seal, it may not be the 1/2 hour job you plan on.