The UK-1 uses a locking blade. Pull the blade fully open and it will click into a locked position. The body of the knife has an indentation adjacent to the locking mechanism. At this point, push the locking mechanism away from the blade and push the knife blade closed.
The UK-1 uses a standard utility knife blade. To change the blade, open the knife fully. Push the knurled knob above the blade, pushing from the logo side of the knife. Pull the blade and remove it. Reverse the process to install a new blade.