To butcher a turtle you start by chopping off the turtle's head. Be careful because the head will still bite even after it is removed from the body and the body will still crawl away after the head is removed. Turtles don't die right away. When the body stops trying to crawl away, dip it in boiling water and scrape off the exterior layer of skin, including the shell. The result will be a bright white carcus, compared to the muddy brown-green you started with.
Next step is to remove the shell.
Cut along grove on each side between the front and back legs. It is the narrowest part of the shell. The tail, neck and all four legs are attached to the top of the shell. Remove from shell and you have the bulk of the meat. However, there will be some meat on the bottom shell and top shell.