All you have to do to download PMX Editor is go to
learnmmd.com/ and one you are the int the top box click "Download"
and scroll down until you find the blue box that says "PMX Editor" once done, click on the blue box and it should take you to a deviant art page. Then, go into the descriptions (you have to scroll down a little ways until you reach "Downloads") once you are there you should see 3 links (they all say external link) click a link and ( it doesn't matter witch one) then download the app from there. Last, if you haven't yet on the deviant art page with the links below the downloaders there should be extra things you will need to download to help the app work. I hope I explained enough! Good luck!