Urgent Administrator Problem

Greetings! I am using Windows Vista Home Premium. I recently downloaded an
upgrade that requires me to uninstall a previous version of the program. When
I go to "Control Panel" and click on "Uninstall or Change a Program," I get
this message, which I didn't see a month or so ago:

"Your system administrator has disabled Programs and Features."

Thus, I can't uninstall the program and install the upgrade, which is an
urgent matter. Can any of the Vista experts help me with this problem? Thank
you.

Rebecca