If you break the seal between the body and the rubber, then the glass and the rubber with an old blunt screwdriver, you'll find that the screen will come out easily, just by feeding the inside rubber lip over the windscreen appeture, again, with old flat blade screwdrivers, takeing your time, is the key thing here, dont be tempted to push the screen at any stage, untill all you have left is the section above the dash, carefully push the screen forwards, then lift the screen out, job done
If you do manage to break the screen, the chances are that it would have broken anyway, on refitting!
Any stone chips that are close to the edge of the rubber are your weak points, so inspect carefully before you remove!
Using a 2nd hand screen rubber is not always a good idea! Firstly, if there are any splinters of glass left in the channel from the origional car, these can cause your newly fitted sceen to crack! Secondly, screen rubbers can go out of shape! if they came off a car that has rust pushing through from under the rubber, fitted to your car, they could leak badly
Tom