No software update

Hello. I'm trying to get my macbook pro (retina 13'', primo 2015) to get the newest software update, but every time i go to the app store to find a new software update, it doesn't show any new update. I currently have OS X El Capitan update, but i need at least the 10.13 update to download a program for my school.

I have tried the app store multiple times, but nothing works!!

What can i do?