These are the basic styles that you will be limited to with the editor. If you have HTMLEditor then you could edit the instance on the update page or insert page to include your own custom css styles. To do this you would need to have HTMLEditor installed, then open up the content insert and update pages and edit the HTMLEditor instance that is on the page. In the interface choose to customize the editor, then go to the style tab to add in your styles. You select the css file with the styles then select from the available styles that appear in the list to set which ones will be selectable when you are using the editor.