First, you need to find out more information about your machine. So do the following:
- On the main MacOS Menu Bar, click on the Apple logo on the upper left hand corner of your screen.
- Click on About This Mac
- Now you should see a window displaying the Overview tap.
In the Overview tap, take note of the following information:
- MacOS name and version
- Your machine model and release year
- Memory ( How much GB of RAM available)
- Graphics (graphic card type)
Keep the info above handy for later.
Now, hopefully your machine is not that old and, it's still being supported by Apple.
So to the easiest way to find out is by doing the following:
- Click on the Apple logo once again
- Select About This Mac
- In the Overview tap at the bottom below you'll see two option: 1- System Report and 2- Software Upgrade
- Select Software Upgrade
- Software upgrade should open the Apple Store app and, it automatically start searching for available updates for both the current version of macOS you're actually running and, any applications installed on your machine.
WARNING
DO NOT MAKE ANY mac OS UPGRADES TO YOUR MACHINE UNTIL YOU CONFIRM THAT IT WILL SUPPORT THE UPGRADE. Updates and security patches to your current mac OS are just fine but upgrading the operating system is a whole different ball game when dealing with an older Apple machine.
Here is where the info from About This Mac is going to come into play.