Myron's tip about the need to unscrew the grey rubber coupling is correct, but I was unable to grab the post and hold it still, even though I was using narrow needle-nose pliers. I just could not get underneath the rubber coupling. I ended up cutting the rubber piece off the steel cord inside the coupling, which exposed the threaded post. I could hold the post stationary from above while I unscrewed the steel cord. My old coupling was stripped and worn out, so it did not matter. A new coupling can be ordered cheaply.
I found that it was not necessary to open the housing of the whole appliance as long as you can hold the post stationery. And even if you can't grab the post from above, opening the housing won't help because it won't come off until the coupling is removed at the top.
If you need to open the appliance for anything else, Myron is right, you need to remove the 4 rubber boots on the bottom to expose the screws. The screws are so-called temper-proof screws for which you need a special screwdriver. The screws are called "pin-in-head-star". But removing the 4 scows is not enough. You also need to unscrew the coupling at the top.