"Error on deleting file or folder" while upgrading to 2.5.14

[Tagin]

Environment: Joomla 2.5.9, PHP 5.4.11 on Windows 2008R2 server with IIS.
(Note that Site Information/DirectoryPermissions reports all directories as "Writeable".)
Attempting to upgrade 2.5.9 to 2.5.14 using the "Upload Package File" method.
Results in the following errors (and system continues to report as being at 2.5.9 - even after system reboot):

JInstaller: :Install: Failed to copy folder \tmp\install_51fac544a0cd4\cli to C:\inetpub\wwwroot\cli
Failed deleting swf-uncompressed.js
Failed deleting swf.js
Failed deleting uploader-uncompressed.js
Failed deleting uploader.js
Failed deleting index.html
Failed deleting uploader.swf
Failed deleting index.html

Installing file was successful.

Joomla! 2.5 Content Management System
Error on deleting file or folder /media/system/js/swf-uncompressed.js
Error on deleting file or folder /media/system/js/swf.js
Error on deleting file or folder /media/system/js/uploader-uncompressed.js
Error on deleting file or folder /media/system/js/uploader.js
Error on deleting file or folder /media/system/swf/index.html
Error on deleting file or folder /media/system/swf/uploader.swf
Error on deleting file or folder /media/system/swf/

[Tagin]

Problem solved!

Although all directories showed as "Writable" in Joomla, the user IUSR (since this is a Windows IIS system) needed write permissions to these directories, and I had previously restricted IUSR rights to read-only.

So, navigating to \inetpub and granting Full Control to IUSR for \inetpub\wwwroot allowed the upgrade to complete properly, and the system now reports it is ver. 2.5.14.

Q: Is is acceptable to leave these Full Control permissions, or should I restrict them back to read-only until the next upgrade?