A 2013 MBPro can upgrade to the latest 10.14 (Mojave), but will not show you an update to do that. You have to download the Mojave installer app, and install that.
Open your App Store. Mojave should appear in Updates, so just click Download. This will take a few minutes to download. The installer will launch automatically when download is complete, and click to continue with the install, which will take another few minutes. Your MBPro will then restart to complete the upgrade. The whole process (depending on the speed of your internet connection) may take most of an hour, and your MBPro will restart on its own a couple of times.
If Mojave does NOT appear in your updates tab, click on the Featured tab, and search for Mojave in that window. You will see the information page for Mojave. Click on the Download button, and run the install when that opens up - same as the above. It just takes some time, so you want to have a free hour to do that upgrade
