1. Turn ratchet-wheel wheel counter-clockwise to loosen locking mechanism.

2. Slide ratchet-wheel assembly past base of handle to remove. 

3. Remove ratchet-wheel dial from the blade. Carefully slide used blade out of the handle and dispose of properly in sharps container. 

4. Insert new blade into channel. Alight with assembly by placing the hole in the blade over the raised mounting point. 

5. Slide ratchet-wheel assembly and blade forward.

6. Turn ratchet-wheel dial clickwise to tighten the locking mechanism.