replace / install tilt-window latch?

i have single-pane tilt-windows. some of the latches are broken or missing. i bought replacement latches at swisco.com, items 26-096 and 26-097 (to see this part goto http://www.swisco.com/catalog/tilt_window_parts.html and search for "26-096").
i cannot figure out how to install this latch short of removing the metal frame which houses the pane. this seems extreme and, in my hands, would probably ruin the entire window.
any suggestions as to how to replace / install these tilt-window latches? i'm sorry but i do not know what type of windows these are -- i cannot find a label.
thanks, - bettyann
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