Her is how to take care of an X-ACTO knife.
Step 2: How to Cut
To cut hold it like a pen then put your other hand in front of the X-ACTO knife. Then cut.
Step 3: Holding
Don't hold it straight up but hold it at an angle. Also don't cut with it leaning on the side. This will break the blade.
Step 4: Replacing Blades
To replace a blade on the X-ACTO retractable first dissemble the pen. Then get a new blade and slide it in. Then rotate the blade until it gets stuck. Finally reassemble. For the classic loosen the tip then pull it out. Last take your new blade slide it in and tighten.