How to update 2015 Macbook to 10.14

I keep getting "(Application) can’t be installed on “Macintosh HD” because OS X version 10.14 or later is required." for every single app I try getting. I have a MacBook Pro (Retina, 13-inch, Early 2015) running Version 10.11.6. I click software update and then it doesn't say there is another update I could do. How do I fix this?

[Re-Titled by Moderator]