What operating system, including version, and browser, including version, are you using?
I'm assuming you mean version 9 or higher. The latest version is 18.104.22.168, available from get.adobe.com/flashplayer. The download location is most likely you're Downloads folder, unless you changed it, or saved it to some other location in the browser preferences/settings. Go to the downloads location, double-click on the installer file (it has flash player in the file name) to launch the installer and proceed with the installation.