how do i update the software on my MAC Pro?

Your profile says you are on macOS High Sierra 10.13.

System Preferences> Software Update does not exist on that OS it

only came in with macOS Mojave 10.14.

Installing a newer OS is called an upgrade.

Which OS you can upgrade to will be governed by which model and year your mac is.

What year is your Mac Book Pro, click on the top left of your screen

and click on About This Mac.

To get information on which OS's you can upgrade to open your Safari

browser and click on the link below.

How to get old versions of macOS – Apple Support

Go to Check Compatibility to see if your mac qualifies for the OS upgrade you want.

Then go to the Download OS section and click on the OS you want to install.

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you want to or are able to install Big Sur, open Safari and click on the link below.

How to upgrade to macOS Big Sur - Apple Support

If you are considering upgrading to Catalina or Big Sur be warned they do not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see

if they are offering 64bit updates.

macOS can be updated on a Mac by going into System Preferences and clicking Software Update. This will update your current version of your operating system to the latest version of that operating system but will not update you from say, macOS Catalina to macOS Big Sur.

To make a jump like that you need to download the new operating system from the Mac App Store.

To find out more, check out this articles from Apple - https://support.apple.com/en-us/HT201541 and https://support.apple.com/en-us/HT201475