Permissions

Hi!
I have had trouble updating my WordPress installation (the automatic update could not write to/update some file directories?)
Anyway, yesterday I did a manual update of the WordPress itself. I gave 755 access to all directories and 644 access to all files.

However, updating plugins and themes through the update page still fails (Error message: The updates cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions. images, languages, 404.php, archive.php, attachment.php, author.php, category.php, comments.php, editor-style-rtl.css, etc.)

Another, more critical problem also showed up after the WordPress update:
When I use “Upload media” it will only upload the selected file when I makes the “target directory” writable by “others” (or, in other words, a 777 permission for the upload directory). As far as I remember it was not like this before I did the manual update of WordPress.
How can I make this work with the 755 permission again?