Updating from El Capitan to Catalina

How to get old versions of macOS - Apple Support.

WD

Before upgrading to Catalina I would recommend upgrading to High Sierra first.

Although Apple says you can upgrade directly from El Capitan to Catalina

people have reported that the install freezes.

This is probably due to the install converting the El Capitan HFS+ filesystem

to the newer APFS file system which later macOS's use.

macOS High Sierra was the first macOS to use the APFS file system

and therefore should install the necessary firmware to ease this process.

One you have installed High Sierra you can then upgrade to Catalina.

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 ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you are considering upgrading to Catalina 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 providing 64bit updates or alternatives.

Use this link in Safari. It will open the Catalina download page in the App Store.