they are damn hard to remove without cracking them in the process.
you need to cut through the glue in one section using a knife. feed some piano wire through the cut and pull the wire all the way around the windscreen in a cutting/filing action. just try not to pull up on the wire thats what cracks its. hard to avoid. especially at the bottom.
most winscreen places will sell you a new one fitted for about $300-350. they even remove it. makes life heaps easier.