The only way to upgrade your mac is to download the macOS Catalina full installer via the App Store.
Check that your mac is a 2012 MacBook Pro, click the top left of your screen and select About This Mac.
These are the MacBook Pros that can install macOS Catalina,
- MacBook Pro (13-inch, 2020, Two Thunderbolt 3 ports)
- MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports)
- MacBook Pro (16-inch, 2019)
- MacBook Pro (13-inch, 2019, Two Thunderbolt 3 ports)
- MacBook Pro (15-inch, 2019)
- MacBook Pro (13-inch, 2019, Four Thunderbolt 3 ports)
- MacBook Pro (15-inch, 2018)
- MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports)
- MacBook Pro (15-inch, 2017)
- MacBook Pro (13-inch, 2017, Four Thunderbolt 3 ports)
- MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports)
- MacBook Pro (15-inch, 2016)
- MacBook Pro (13-inch, 2016, Four Thunderbolt 3 ports)
- MacBook Pro (13-inch, 2016, Two Thunderbolt 3 ports)
- MacBook Pro (Retina, 15-inch, Mid 2015)
- MacBook Pro (Retina, 15-inch, Mid 2015)
- MacBook Pro (Retina, 13-inch, Early 2015)
- MacBook Pro (Retina, 15-inch, Mid 2014)
- MacBook Pro (Retina, 13-inch, Mid 2014)
- MacBook Pro (Retina, 15-inch, Late 2013)
- MacBook Pro (Retina, 15-inch, Early 2013)
- MacBook Pro (Retina, 13-inch, Late 2013)
- MacBook Pro (Retina, 13-inch, Early 2013)
- MacBook Pro (Retina, 15-inch, Mid 2012)
- MacBook Pro (15-inch, Mid 2012)
- MacBook Pro (Retina, 13-inch, Late 2012)
- MacBook Pro (13-inch, Mid 2012)
Open your Safari browser and click on this link,
How to get old versions of macOS – Apple Support (UK)
If your mac can install Catalina go to the Download OS
section and click on macOS Catalina.
This will redirect you to the App Store Catalina download page.
It should say Get or Download.
This will download Install macOS Catalina.app to your Applications
folder it is about 8.26GBs in size.
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 Catalina.app.
Move it to the Trash, empty the Trash.
Restart, click on the link again, the App Store should say ‘Get' or 'Download'.
As you are considering upgrading to Catalina or be warned 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/ then contact the developers of the software to see
if they are offering 64bit updates.