That window looks just like two of those in our cottage, and they are quite old. I think they are Andersons. Anyway, IIRC, with one side opened onto the inner track, you lift the window frame upward and pull the bottom edge inward toward you. Be careful, as they have some weight. The other side would come out the same way, once moved toward the center a bit to free it from the side. If you wish, I could verify this, but I won't have a chance to do so until Wednesday.
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