To use the 5 desktop downloads you get with the Premium Security or Business Premium plan, you must be on one of the following operating systems:
PC: Windows 10, Windows 8, Windows 7 Service Pack 1, Windows 10 Server, Windows Server 2012 R2, Windows Server 2012, or Windows Server 2008 R2
Mac: Mac OS X 10.10
If you are running a different operating system, remember that you can still use Office Online, browser-based versions of your favorite Microsoft tools like Excel, Word or PowerPoint, which are included with the Online Essentials or Business Premium plans.