There is no user administration UI at the moment, but there are plans to add one.
Currently you can delete users by accessing their profiles while logged in as an admin. The Delete command is in the drop-down list to the right of the profile card. So if you wanted to delete a user named "Foobar" from your forum at example.com, you would navigate to this URL ...
http://example.com/u/foobar/
... then use the Delete command to delete that user. Or Suspend to suspend them indefinitely, if you prefer.
