Before you begin it should be noted that this breaks search function with regular search bar, BUT if you use a Start Replacement like I do, Star10, You will still have a working search function.
Via WinAero(Detailed guide, not Direct DL Link) Just download the Zip (Uninstall_Cortana_[winaero.com]_1802.zip) and Run the CMD (Uninstall Cortana.cmd) as Admin.
The zip contains 2 files:
It is free, install_wim_tweak.exe can also be gotten from Legolash2o's page linked below and you could create your own CMD if you are leary of running downloaded CMD's as Admin.............
Read Article, apparently it is hard to reinstall!
"Behind this trick is an application called WIMTweak which manages Windows Packages and allows you to hide/unhide them from the Windows image (WIM) file. It works on offline images as well as online. WIMTweak was created by MSFN user Legolash2o, so credits for this awesome tool go to him." --WinAero
Legolash2o's page @ MSFN with more details on WIMTweak
The Contents of the CMD are: (But most of the Magic happens with WIMTweak)
cd /d "%~dp0"
echo Uninstalling Cortana...
install_wim_tweak.exe /o /l
install_wim_tweak.exe /o /c Microsoft-Windows-Cortana /r
install_wim_tweak.exe /h /o /l
echo Cortana should be uninstalled. Please reboot Windows 10.
The source code for install_wim_tweak.exe has been posted on GitHub by another user @ https://github.com/shiitake/win6x_registry_tweak