Removing Steel Basement Windows
I have removed these before. A cut at the bottom bar, which is not anchored into the sill the way the sides and head is. When cut, the 2 bottom corners can draw in, allowing the flanges on the sides to begin to withdraw from the groove they are mudded into. You may want to nick the upper inside corners to make it easier to bend inwards. They might even snap there for you too. If they only bend in at the bottom, that will still have the lower corners raised above the bottom masonry sill by a few inches. With that the head that is keyed in at the top can be tapped down to release it, one corner at a time.