When on blade used up, how does one load the next blade on the task force box cutter?

Pull blade plunger from sleeve, remove razor blade, replace razor then slide blade plunger back into sleeve

Pull the old blade straight out. Take the replacement blade (there are two in the handle) Holding it by the side, slide it in the silver blade holder track. The end with the hole in it goes in first towards the black adjustment button. If it does not lock in just forward of the black blade adjustment button there is a flat spring with a detent that will lock into the hole on the end of the blade. If it doesn't lock, take a flat item, small screwdriver, (a paper clip will work) and life up the spring and slide the blade in until it locks.