you have to put a very small ,say 1/16-inch pin punch under the blade ( into the hole the windage screw came out of) must take the pressure 'off' this spring to release the blade...as noted above, the newer sights and the sight body have a small "divot" that you need to align to remove the sight blade...if the blade has the divot and the body does NOT, you have to remove (file down) the divot in the sight blade to use in an "old model" sight body.....these divots were done to keep the blade from jumping out of the older style sights, happened all too often with hot loads, or worn, loose sight parts.........
reverse for the install, use the pin punch to decompress the spring while inserting the blade............