If you already uninstalled Office 2016 under Apps & features and Office 365 won't load or you receive a message saying "We're sorry, Office Click-to-Run installer encountered a problem because you have these Windows Installer-based Office programs installed on your computer: Microsoft Office 2016" follow these steps:

Go to Helix > Programs > Office 365 > Diagnostic tool Outlook Office 365 > SetupProd.exe 

After installing the Microsoft Support and Recover Assistant, click Office & Office Apps and click Next

At the "Select the problem you are having" page, select "I have Office Installed, but I'm having trouble uninstalling it." Click Next

At the "Uninstall Office Products" page, select Microsoft Office 2016 and click Next

This will completely uninstall Office 2016 and it will have you restart the computer. You will then be able to install Office 365.