Clearly I did this before because I have lists showing up when I go to twitter.com, but I can't figure out how to edit them now (i.e. move people / add people / delete people from the lists).
Here are the new steps with screenshots
Alternatively, you can go the user's page and decide and remove that person from there
The UI ideally should hint that "Add to List" also includes remove from list.
Click on any of your twitter lists on the left side of your home feed., click on the view the list page link. Click on following to delete people from your list.
To add: Go to any person's page and click on the menu on the left and add to any of your lists