Twist off all the legs, small and large. Sometimes the feathery grey gills called “dead man’s fingers” will come out with the large claws - these are not good to eat and will make you feel sick so make sure to discard them. Most of the time they will be in the body.
Put the crab on its back so its tummy is upwards. You will see the crab’s two eyes, and below these there are two small flaps. Move these aside and push down on the slightly softer shell underneath with both your thumbs. Push hard to crack through, then you can pull out the middle section of the body. Inside it looks like a bit of a mess, but you can eat everything EXCEPT the “dead man’s fingers”. Don’t worry, they are so distinctive you can’t miss them - they look just like feathers. Pick through the rest of the meat and put it in a bowl. This is where you will find most of the brown meat.