I am doing both my cargo windows right now. What I found helpful is to slip a flexible putty knife under the inner side of the rubber seal. lift the seal up toward the top of the body flange, as Don foster has said.

As you do this, use a large, flat screwdriver to nudge the ruber gasket over the top of the flange.

Work from one bottom corner to the other. Extend this about six inches up the pillars on each end.

By this time, the window should push out from the inside. Have a helper outside to receive it, or, stand in the hatch to pass one corner out to yourself.

This is tedious and time consuming. Have patience. And, don't try to lever things so the windows cracks. (It takes a lot of punishment, but still, ovserve caution)