how can I update safari in my Mac

Safari is updated along with macOS. To learn how to do that, please read How to update the software on your Mac - Apple Support.

Anticipating your next question, what if Safari is already the latest version for your Mac, macOS cannot be upgraded beyond macOS 10.13 as shown in your profile information, and you are unable to load certain websites because they are complaining Safari is too old. Your alternatives are to use another browser with the security features they need.

I recommend Brave:

https://brave.com/

If Brave is not an option for your Mac, Firefox is another possible choice:

https://www.mozilla.org/en-US/firefox/new/