A simple PUT request to update the order.

PUT-SimpleOrder

//PUT /admin/orders/#{id}.json
{
  "order": {
    "id": 450789469,
    "email": "new_email@example.com",
    "line_items": [
      {
        "id": 12412415,
        "title": "Shiny Black Boots",
        "price": 82.99,
        "quantity": 1
      }
    ]
  }
}