upgrade El Capitan

Back up your data, check your applications for compatibility, and if your Mac is a 2012 or newer model, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphic card, click on Mojave. Otherwise, no.

(201344)

All these Macs can be upgraded to 10.14 as well (x,y is machine ID reported in Apple menu -> About This Mac -> System report):

MacBook early 2015 8,1

iMac Late 2012 12,1

MacBook Pro Mid-2012 9,1

Mac Mini Late 2012 6,1

MacBook Air Mid 2012 5,1

See this tip on how to:

https://discussions.apple.com/docs/DOC-13571