How to change user fields with API

You can make a GET request to /admin/customize/user_fields and it will return a list of user fields:

{
  "user_fields": [
    {
      "id": 2,
      "name": "Favorite OS",
      "description": "What is your favorite Operating System?",
      "field_type": "text",
      "editable": true,
      "required": false,
      "show_on_profile": true,
      "show_on_user_card": true,
      "searchable": false,
      "position": 1
    }
  ]
}