In most cases, a clean install is not required when installing Flash Player. The Flash Player installer will upgrade previous installs without having to uninstall first. However, if you find you're running into problems or would like to downgrade to a previous version, the following steps and video should help.
Windows
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Restart Windows. If you are using Windows 8, please skip steps 4 and 5.
Delete all remaining files and folders located in the following directories. (tip: copy and paste these paths into the path bar in an Explorer window)
C:\Windows\system32\Macromed\Flash
C:\Windows\SysWOW64\Macromed\Flash (if you are using a 64-bit system)
%appdata%\Adobe\Flash Player
%appdata%\Macromedia\Flash Player
Verify that the files “FlashPlayerCPLApp.cpl”, "FlashPlayerApp.exe", and "FlashPlayerInstaller.exe" in C:\Windows\system32\ (for 32-bit systems) or C:\Windows\SysWOW64\ (if you are using a 64-bit system) have been deleted. If any of these files cannot be deleted, use Unlocker to remove them from your system.
Note that you may not see the .exe suffix on FlashPlayerApp.exe and FlashPlayerInstaller.exe, depending on your Explorer settings.
Close all browser windows, mount and run the uninstaller
Restart OS X
Delete all remaining files and folders locating in the following folders:
\Library\Internet Plug-Ins\Flash Player.plugin
\Library\Internet Plug-Ins\flashplayer.xpt
~\Library\Preferences\Macromedia\Flash Player\
~\Library\Caches\Adobe\Flash Player\
At this point, Flash Player should be fully removed from your system. To download the most recent version of the Player for installation, please visit http://get.adobe.com/flashplayer
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