My mac Desk top cannot update new software big sur

Hello, Angela bancroft.

How to Upgrade to  macOS 11 Big Sur:

❗️– Backup your data. (You’ve been warned.)

Learn How to Back up your Mac with Time Machine:

click > https://support.apple.com/en-us/HT201250

❗️ – IMPORTANT! Starting with Catalina, 32-bit apps will no longer work.

Get this free utility to check the compatibility of your apps:

click > St. Claire Software – Go64

📚 – Check Compatibility of your Mac with newer versions of macOS.

Learn how to upgrade macOS:

click > https://support.apple.com/en-us/HT211683

These Mac models are compatible with macOS Big Sur:

• MacBook introduced in 2015 or later

• MacBook Air introduced in 2013 or later

• MacBook Pro introduced in late 2013 or later

• Mac mini introduced in 2014 or later

• iMac introduced in 2014 or later

• iMac Pro

• Mac Pro introduced in 2013 or later

To find the details about your Mac model, click the Apple  icon at the top left of your screen and choose About This Mac. 

✅ - Download the macOS 10.11 Big Sur upgrade installer here:

click> https://apps.apple.com/us/app/macos-big-sur/id1526878132?mt=12

(Don’t use FireFox for this link)

The download will place the "Install macOS Catalina" application in the Applications folder. Double-click the installer to begin the upgrade process. 

CORRECTION–

The last sentences of my previous post should read:

"The download will place the "Install macOS Big Sur" application in the Applications folder. Double-click the installer to begin the upgrade process."

If your iMac is older than mid 2014, it’s not compatible with BigSur.

To check which Mac you have: click on the Apple icon, About this Mac