Log into your Office 365 mail at Office 365 login
Left click once on the gear icon on the top right.
Left click once on the Office 365 settings.
Then left click once on Software
Once you get to the software page, click on the Install button .
Go to the download folder on your computer,find the setup program, and double click on it to begin the installation.
If a dialog box appears asking you if you wan to run this program, click Run and then follow the onscreen directions to complete the installation.