Rear window in 95 C1500

Hi,

I'm probably making a bigger deal out of this then need be, but I need to reseat the rear window in my 95 C1500, since one corner is out and won't stay in. I have a silicone substance to keep it in place, prevent leaks, etc, but I'm having trouble getting the window out since some of the old glue is still in tact. I was wondering would I just be able to take a knife with a thin blade and cut through the glue?

Thanks.