It's as easy as that. There'll be a button. Push it. Confirm it. ZAPP, your pad will be deleted. Removed. Gone, with all its history... :')
On the command line, run
npm install ep_push2delete.
Alternatively, browse to
http://<etherpad>/admin/plugins, search for
ep_push2delete and click install.
The plugin takes effect, after restarting the server.