Skype for Business on my MacBook Air
I want to use Skype for Business on my MacBook Air. I have downloaded the relevant software.
The operating system on my MAC is OS X Yosemite version 10.10.5 and when I try to run the relevant software, I'm told that the operating system will not support it.
How do I download and install a later OS for the MAC? When I try from "About this MAC" menu, I am not given an option to upgrade the operating system.