I don't think Superpowers provides an easy way to do this through the ui. What you can do, however, is:

Go to where Superpowers is install [ it depends on your operating system I think, look here: http://docs.superpowers-html5.com/en/getting-started/setting-up-superpowers ]

You will see 2 folders. One called 'app', and another called 'core'. Go into 'core'. Then, go into the folder called 'projects'.

Select the project folder that you want to remove, and delete it.

Hope this helps!