How can I update my office Mac2011?

You will need to acquire Microsoft Office 2016 (no longer for sale, and no longer supported by Microsoft), Office 2019 (current), the upcoming Office 2021, an Office 365 subscription, the free LibreOffice package, Google Docs or similar service, or for many Office documents Apple iWork Pages, Numbers, and Keynote.

You can purchase Office 2019 or an Office 365 Subscription directly from Microsoft, and purchase an Office 365 Subscription from Microsoft via the Apple App Store. (I don’t know off-hand if you can buy Office 2019 from Microsoft via Apple.)