It took me a bit but I did find out how to do this.

Create your numbered list

1. one
2. two
3. three

Then right click in the list and select list properties, change the type.

1. one
2. two
3. three

 edit:

The above looks ok in the editor but does not display. It has set the type to 'a'
<ol type="a">

I found a solution to the ordered list problem

remove these lines from the portals/_default/default.css file

OL LI   {
    list-style-type:    decimal;
 }

OL OL LI    {
    list-style-type:    lower-alpha;
}

OL OL OL LI {
    list-style-type:    lower-roman;
}

The css file is overiding the tag set by the editor.