(Assuming you mean "edit comments:" If someone's replied to it, even if the comment's subsequently been deleted, comments are no longer editable. Otherwise, it's as simple as clicking the "Edit comment" button; if you don't see it either you don't have permissions (can free users edit comments? It was at least once a paid-only feature), the comment's been replied-to (see above), or the page style doesn't support it (try adding ?style=light to the URL).)