Cortana is search engine built in coming to Win 10, Its Helpful for few reasons but still if you want to disable Cortana Win 10 then Follow the steps below.
Just follow these 3 Steps to Disable Cortana in Win 10
Step 1 : Go to the Settings
There are many ways to go in the settings, Like you can right click on windows menu or just click on window menu button and from the left bar click on settings button.
Step 2 : Search for Cortana
Now on the setting option you can Search for Cortana, Click on Cortana & Search Settings as shown in below image.
Step 3 : Disable Options for Online Search, or there are more other options available upto you whatever you want to keep or not.
Final Words : There more settings and options related to Cortana, you can switch, disable or enable in these settings.