Norton antivirus is asking for me to update Safari. How do I do that?

See here: link-> Update to the latest version of Safari - Apple Support

As noted, Safari is able to be upgraded when the operating systems upgraded or updated. It is installed as part of the Mac's operating system. Regarding Norton, no Mac needs an antivirus app installed. it has it sown built in protection. Norton WILL slow down your computer and likely cause other serious problems. It should be removed using Norton's uninstaller app.