What is telling you that Flash needs to be updated? If you're seeing something on a website telling you this, chances are good that it's a scam and that if you install the thing it links to that you'll be infected with malware and junk software.
Also, note that Flash has been the cause of serious malware infections on the Mac in the past, and has suffered from security vulnerabilities almost every month - sometimes multiple times per month - for years. It really should not be used any longer. Any site still using Flash should be considered to be horribly outdated and insecure, and should be avoided at all costs.
The best thing you can do is uninstall Flash and never look back.
https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html