Thank you for posting your concern here at the Microsoft Community forum. Let me assist you with your concern.
You cannot uninstall Cortana on Windows 10 Technical Preview 2. However you my try turning it off from settings.
Left click on Search box.
Click Sandwich icon on Top left.
Click Settings and Turn off
the button under “Do you want Cortana to work for you?”
This will turn off Cortana on your user profile. If you want to remove
Search box in taskbar, right click on taskbar and click
Search and choose Disabled.
Hope this helps. If you need further assistance with Windows, let us know and will be glad to help.
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