Once you remove the door panel, removing and replacing the door check strap is fairly easy.
I am assuming that the strap portion, as it is called, broke in half? This is the most common way it fails. If so, follow along:
The first step is to use a pair of needle nose pliers and/or a screw driver to remove the C-clip that holds the pin in place where the strap connects to the body of the car. With the c-clip out, you can then use a small punch tool to tap the pin out towards the top of the door. This will let you remove the throw away the broken piece of the strap.
The next step is to remove the door panel, using the guide you referenced.
With the door panel off you can now remove the three bolts that hold the rest of the door check part. There should be one bolt at the end of the door check, furthest from the strap, on the part of the door usually covered by the panel. Then there will be two more bolts on the inside edge of the door, near where the strap protrudes out.
Once you've removed those three bolts the door check should come right out.
Now you'll just need to install the new part in the opposite order - bolt it in to the door, and then connect the strap to the body with the pin and insert the c-clip to hold the pin in place.
Good luck and let me know if you have any other questions.