As of Windows 8, Microsoft embeds Flash Player in Internet Explorer, and Edge browser in Windows 10, and all updates are released by Microsoft via Windows Update. Microsoft also posts links to the updates at Microsoft Security Advisory 2755801. Just click on the KB article link for the latest update and then download the update for your OS and system architecture.
If you're referring to Flash Player fora different browser (except Google Chrome, which also embeds Flash Player), launch the browser and navigate to https://get.adobe.com/flashplayer. Download the installer, making note of the save-to location. After the file downloads, go to the save-to location double-click on the installer file and proceed with installation.
Also, if your favorite website is telling you that you need to install Flash, but you're on IE or Edge, the following will be useful:
First, confirm that ActiveX Filtering is configured to allow Flash content:
You can try to work around these issues by using Compatibility View:
If that is too inconvenient, using Google Chrome may be a preferable alternative.