|if you're at least a local admin on the machine, open the C:\ drive and Right Click the "World of Warcraft Trial" folder.|
front the Right Click menu, click "Properties" and then click the "Security" tab.
i suspect "USERS" should already have Read/Execute, List Folder Contents, and Read. just click the "Allow" box next to Modify, and you've given all local users the ability to change everything in that folder.
of course, if you're really an admin, you should already have Full Control to subfolders on the C:\ partition, unless someone really messed up your permission inheritance.