Operating System Version Numbers, April 2016
How To Check Your OS Version and Perform an Update
Click the at the top left of the Finder and select “About This Mac.” Click the “Software Update” button.
Open Settings and select General and then “Software Update.”
Open Settings and select General and “About.” To check for an update open Settings, then System and choose “Software Updates.”
On your iPhone, open the Watch app and select General and “Software Update.”