Getting one of these screens while trying to upgrade or install a theme through the administrative interface on your WordPress.org blog?

The fix is easy enough. If you’re running Apache2 as your webserver, you need to give whichever user Apache2 is running under (www-data by default on Debian) ownership of your WordPress directory:

chown -R www-data:www-data [your directory path here]

If leaving Apache with write makes you queasy, simply chown back after the upgrade:

chown -R [previous user]:[previous user] [your directory path here]