Make sure it's empty. Put the safety ON.
Lock the slide back, and turn down the disassembly lever on the left front frame.
Hold the slide under control, and press the slide lock, releasing the slide.
Move the slide forward and off the frame, (the hammer will drop, as the slide is removed, don't worry this is normal).
Turn the slide over and look at the rear of the barrel. You'll see a pin sticking out of the lock block. Push the pin in and the lock block will pop up.
Pull the barrel forward out of the slide.
Pull up the rear of the lock block to remove it.
Unscrew the grip screw and remove the grips to expose the lock work.
Further disassembly is only recommended if you can find detailed instructions like the NRA Disassemble Guides.
To reassemble:
Put the front of the lock block into the groove in the barrel, and press down on the rear of the block.
Hold the block down and push the barrel into the slide.
Start the slide onto the frame. Look inside the rear of the frame and you will see two safety levers and the ejector. Press these down as you move the slide back.
Pull the slide back and hold it open with the slide lock.
Turn the disassembly lever back up.