(defun dired-up-directory-in-same-buffer ()
  ;; Open the parent directory, but do it in the current buffer.
  (interactive)
  (find-alternate-file "..")
)

(defun dm-hook()
  ;; Redefine some functions so that dired will re-use the current
  ;; buffer whenever possible.
  
  ;; Was dired-advertised-find-file.
  (define-key dired-mode-map (kbd "<return>") 'dired-find-alternate-file)

  ;; Was dired-up-directory.
  (define-key dired-mode-map (kbd "^") 'dired-up-directory-in-same-buffer)
)

(add-hook 'dired-mode-hook (function dm-hook))