Or an upgrade is a term that describes adding new hardware in a computer that improves its performance.

Hardware upgrading is the replacement of new hardware with the old versions. Using an earlier Time Machine backup provides a simple way to upgrade to MacOS High Sierra. This tutorial shows you how to upgrade your MacOS High Sierra (10.13) beta back to MacOS Sierra (10.12.x) or OS X El Capitan (10.11.x) using Time Machine to restore a previous backup. As you are on El Capitan and you want to go to Sierra that is called an 'upgrade' and you can only upgrade to macOS Sierra via the App Store, the version that is available at the moment is 10.12.4, which is the full installer. 10.14 Mojave will not be supported for your machine so it looks like High Sierra will be the final version for you.

I am fairly sure that El Capitan already has no more updates (3 years old), as any new issue will make Apple just say update to the latest release. High Sierra is available for download from the App Store. Here's how to upgrade from El Capitan to Sierra.

In computing and consumer electronics an upgrade is generally a replacement of hardware, software or firmware with a newer or better version, in order to bring the system up to date or to improve its characteristics. Upgrading is the process of replacing a product with a newer version of the same product. Also, you will learn that what is an upgrade and how you can do upgrade from on OS to the another version of OS. macOS Sierra 10.12 is the latest released version of Mac operating system right now. In this article, you are going to learn that how to upgrade Mac OS X El Capitan to macOS Sierra 10.12. Upgrading from one operating system to the another OS is the way of installing Windows or Mac operating system.

El capitan vs sierra memory usage