To delete a page, click "pages" in the wiki to get to a screen that lets you run a query to list the pages in the wiki. You probably want to select "orphaned" and then click "view" to get a list of not-linked-to pages. Click the X next to the page you wish to delete.

Note that when you get down to one orphaned page, it won't let you delete it, giving you a message like "can't delete last page". You'll have to re-query after selecting "all" pages to get that final page.

(Pardon the late reply, I'm a newbie to wikis, trying to figure out if it's worth using this module. Your question made me look so I thought I ought to reply.)