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.
If you are viewing this page in Firefox and Flash Player is not working, please click here for an HTML5 version of this video: YouTube HTML5 HD Link
select the OS and browser you want to install Flash Player for
Close all browser windows, and any other application that may use Flash Player (e.g. instant messaging clients, etc)
Run the uninstaller downloaded in step 1
If you are using Windows 8, 8.1, or 10 do NOT perform steps 6 and 7.
Delete all remaining files (except for the FlashInstall.log file) 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 - do not delete the FlashInstall .log file(s)
C:\Windows\SysWOW64\Macromed\Flash (if you are using a 64-bit system) - do not delete the FlashInstall .log file(s)
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.