420 Aft Cabin window is STUCK

I own a 1999 aft cabin. I was attempting to open the rear window/hatch in the rear stateroom. I'm guessing that it has NEVER been opened before and it is stuck. I'm afraid it will break if I apply too much force. Any idea what I can do to get it open before I need to use it in an emergency.

Not familiar with the particular window. We freed one on a boat at our marina by taping off the area and spraying WD40 around the inside and outside of the seal while using a PLASTIC putty knife to help it get in as far as we could. Just kept working at it and it eventually broke free. Good Luck.