How do I upgrade / download to macos 10.15.0 the full version?

Do NOT upgrade until you have made a Time Machine or other backup of your startup drive.

How to Upgrade  macOS:

The macOS version you can upgrade to depends on the year your Mac was released.

Click the  (Apple) menu at the top left of your screen and choose About This Mac.

macOS 10.15 Catalina is compatible with the Macs listed here:

https://support.apple.com/en-us/HT210222

❗️ – IMPORTANT – Backup your data, now, before you attempt an upgrade.

Learn How to Back up your Mac with Time Machine:

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

❗️ – IMPORTANT – NONE of your 32-bit apps will work in Catalina or Big Sur.

https://support.apple.com/en-us/HT208436

Before you upgrade, use this free utility to check the compatibility of your apps:

Go64: https://www.stclairsoft.com/Go64/

🖥 – Check the compatibility of your Mac with newer versions of macOS.

https://support.apple.com/en-us/HT201475

✅ - Using Safari only, download the macOS upgrade installer app:

Click > Catalina.

Once downloaded, double-click the installer app in the Applications folder to begin the upgrade.

Don't upgrade to Catalina until you have downloaded and run the free Go64 application that will show you all of your current 32-bit applications/drivers that are not supported on Catalina which only supports 64-bit applications, printer, and scanner drivers. Check with the third-party application and driver vendors for products supported on Catalina.