That file on my site is set for permissions 644.
Possibly your browser cache is interfering with the upgrade.
Maybe try a different browser to rule it out.
Also the docs state to upload that folder from the new zip file, Did you do so?
styles/images/
Yes. Typically what I do is unzip the version into its own folder, remove the directories per instructions, and then cp -R the entire structure into the forum folder.
