Fatal Error when doing Upgrade

Hello – Today (July 6, 2013) I received a message at the top of my screen to upgrade. I hit the button to upgrade and received the following error message.

Fatal error: Cannot redeclare install_wtwp() (previously declared in D:\Hosting\11164370\html\wp-content\install.php:36) in D:\Hosting\11164370\html\wp-content\install.php on line 93

I now receive this message when trying to access my dashboard or edit my site.

I appreciate your help as I am not very technically savvy.
Allison