Go to Insert -> WebAssist -> Preset Manager.
from the product dropdown list, select CSS menu Writer - Menu Themes. Select the theme you wish to delete and click the remove button.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.