To change the blade on an Allway 1-1/2" single-edge razor scraper, typically you slide the blade holder assembly out from the back of the housing. Remove the dull blade, insert a new one into the holder (holding only by the blunt spine), and slide the assembly back until it locks. If your model has a push-button mechanism, press the button to release or retract the blade. Always handle sharp blades with extreme caution.