dosen't support

The model and year of your Mac will determine which macOS you can upgrade to,

read the following links.

How to upgrade to macOS Mojave - Apple Support

How to upgrade to macOS High Sierra - Apple Support

How to upgrade to OS X El Capitan - Apple Support

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.

macOS Catalina 10.15 was released recently, the latest version of macOS.

If you are considering upgrading to Catalina be warned that it does 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/. Once the list has been created you can then

contact the developers of the apps to see if they provide 64bit updates. 

How to upgrade to macOS Catalina – Apple Support

To find out, if your hardware supports Catalina, check this article:

...

If you're using one of these computers with OS X Mavericks or later,* you can install macOS Catalina. Your Mac also needs at least 4GB of memory and 12.5GB of available storage space, or up to 18.5GB of storage space when upgrading from OS X Yosemite or earlier.

MacBook introduced in 2015 or later

MacBook Air introduced in 2012 or later

MacBook Pro introduced in 2012 or later

Mac mini introduced in 2012 or later

iMac introduced in 2012 or later

iMac Pro (all models)

Mac Pro introduced in 2013 or later

* To upgrade from Lion or Mountain Lion, first upgrade to El Capitan, then upgrade to Catalina. To find your macOS version, Mac model, memory, and storage space, choose About This Mac from the Apple menu . If your Mac isn't compatible with macOS Catalina, the installer will let you know. View the complete list of compatible computers.

...

copied from: How to upgrade to macOS Catalina - Apple Support

If Catalina is not supported by your hardware setup, you could install other macOS versions:

How to upgrade to macOS Mojave - Apple Support

How to upgrade to macOS High Sierra - Apple Support

How to upgrade to macOS Sierra - Apple Support

How to upgrade to OS X El Capitan - Apple Support