I went to the Fedora documentation for help.
To change the desktop theme, choose System → Preferences → Appearance. The Appearance Preferences window appears with the Theme tab selected. To change the theme, select one from the list, the theme will be applied automatically.
Fedora's repositories include many other themes that you can install, in the gnome-themes-extra package. You can install gnome-themes-extra by either using the "PackageKit" or on the "command line" by using Yum. Refer to Chapter 18, Managing software for instructions.
This page says that the Gnome Tweak Tool has been approved but has not yet been implemented-
Wonder if that's why it's not running like it should? But over an agreement,something is not right or I seriously misunderstand--
Hope this helps-