advance the blade to it's fullest with the thumb slide.
push in and hold the little black button up by the blade.
carefully with a gloved hand preferably wiggle and pull the blade out.
Get a new blade
push in and hold the little black button up by the blade again.
carefully reinsert the blade in the tip of the knife by wiggling and pushing the blade into place.
let go of the black button and ensure that the blade is secure and in the right place.
I hope that helps!
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them