Flip the window upside down. then in the channel that holds the lower gasket you'll see tiny screws in the corners. with luck, they're not complete blobs of rust anf you'll be able to remove them. I'm siting here thinking that there are screws on the sides too. anyway, that will release the lower channel from the glass, then you gently pull the sides out a bit and the upper piece should come loose from the glass.
It's just a compression fit with the "gasket" keeping the glass snug. it should not be glued with anything very strong. (except age)