Short answer: By clicking on "delete".
Slightly longer answer: You probably can't, because you have no "delete" button.
Even longer answer: Even if you had a delete button, then pedantically speaking, you could not really delete pages anyway. MediaWiKi never really deletes anything, it only hides content. Everything that is deleted can be undeleted, so "delete" is actually the wrong word.
Which page do you want to be deleted?