Those windows are slid into slots in the block on both sides, put in before the wood was installed above them. So to get them out you have to cut through the steel framing ( the bottom is easiest) and "fold" the frame inward pulling the sides of the frame out of the slots in the concrete blocks, no easy job. Or you could build a thin wood frame over them, but that reduces the size of already small windows, and you can't use standard window size.

3 options>>>

- double-pane insulating windows available from some manufacturers. Get the nearest size and fill in around it with wood on installation.
- reuse existing windowframes with panes replaced. A rubber moding -edged piece of plexiglass cut to size to jam into the window opening would act as an economic but effective air insulating layer.
- brick in the window opening, refinishing both inside and outside to match surrounding existing materials & colors.

tip>
hide a doorkey inside a jar under a rock in the bushes,
against lockouts.