How to disable Cortana in Windows 10 (Anniversary Edition)

Click Start, type gpedit.msc and hit enter. Navigate to Computer Configuration > Administrative Templates > Windows Components > Search. Locate Allow Cortana and double-click on it to open the relevant policy. Select Disabled. Click Apply and OK to turn off Cortana.

Source

• http://betanews.com/2016/07/26/cortana-unkillable-in-windows-10-anniversary-update/