I don't know about your specific boat but the usual arrangement is that each of the perimeter pieces of the frame are joined together by a small aluminium plate which can only be unscrewed when the complete window is removed, so no, you can't just remove that top frame. If you slide the window open, in the top groove there is probably a plastic/rubber sealing strip that the glass runs in. If you can remove that strip (it may be bonded in) you MAY then have enough clearance to raise the sliding glass upwards enough for the bottom edge to come out towards you. You may well damage that top plastic/rubber strip so suggest you source another length before you start. If this does not work you will have to remove the whole window so you can completely dismantle the perimiter frame to get the sliding part out and then rebuild.
