I have IMac 21.5 inch macOS Sierra 10.12.6 version I need to have 10.13 or later to install Microsoft package. What do I need to do to update my version

Any Mac that can run Sierra can also run High Sierra:

Get macOS High Sierra

Use Safari for the download.

Easy, please read How to upgrade to macOS High Sierra

Look into the Free LibreOffice, it handles MS Office files…

https://www.libreoffice.org/

Apple macOS (Mac OS X)

The software and hardware prerequisites for installing on a Apple macOS computer are as follows:

• LibreOffice 6.3.x: macOS 10.10 (Yosemite) or higher
• LibreOffice 6.2.x: macOS 10.9 (Mavericks) or higher
• Intel processor
• 512 MB RAM
• Up to 800 MB available hard disk space