Hi, slightly depress the knurled button and you can release the catch holding the blade in place and remove the blade. To insert a new blade [cut resistant gloves recommended] depress the button and insert the blade and then release when the catch has engaged in one of the u-shaped notches in the top edge of the blade.

There is a video demonstrating changing the blade on S0305, here’s the link: https://youtu.be/RHyy77UAPRE (forward to 0.52 secs in)

I trust that this assists?