Earlier this year Apple at it's developer conference announced the new software version dubbed as the MacOS Sierra which comes with built-in Siri. After months of beta testing the new software is now finally ready for general public.
You can download this new version of MacOS from here. But to download it you need to have a good internet connection as it's going to be a 4.77GB download.
The update will brings many new features including Siri is built-in (as we mentioned above), Auto Unlock lets you log in faster, Apple Pay is available in Safari, and tabs are now a part of every app.