Adobe has an official "Uninstaller" for its Flash Player, which you can download here:
Download the small uninstaller program - preferably right to your desktop.
Close ALL browsers and any other running programs which might use Flash.
Run the uninstaller - it's simple and quick.
Once the uninstallation process has completed, reboot your computer.
Go back to the link above, and click on step 4 -"Verify that uninstallation is complete."
You should receive a message that Flash is not installed on your computer.
You can now go back to the adobe website and download a fresh copy if the installer for the latest version of Flash.
Make sure all your browsers are closed before you run the installation.
After the fresh installation - go back one more time and verify that the latest version of Flash is running on your computer.
Hope this helps.