eNewsletter edit newsletter hmtl switcher not showing

When I go in to edit the only newsletter I have created so far, I can't switch to the source code to change some of the styling I want to change. I believe I could see it when I was creating the newsletter the first time.... but can't see it now.

The font in my newsletter is coming out too tiny, so I really just need to change the font size. This time, anyway.

Thanks!