Board Thread:Support Requests - Getting Started/@comment-26462701-20151116020710/@comment-26437440-20151116021248

You can create a wordmark in a photo editor such as Gimp, Photoshop, or paint.

I thiiiiiink the limit is 250px wide and 65px tall. Once you've created one to that size, you can upload it through the theme designer available on the admin panel.