Windows 10 comes with pre-installed windows defender (known before as Microsoft Security Essentials), but there are lots of other antiviruses much better than windows defender, and free like: 360 Total Security or Roboscan.
Note: Before we proceed install an antivirus program of your choice because after disabling the default one you will leave your PC at risk .
1. First click on Start then type gpedit.msc and open it from the results.
2. Then navigate to Administrative Templates → Windows Components → Windows Defender and double click on Turn off Windows Defender.
3. In the pop up window you need to select Enable and then click Ok, restart your PC and it should be removed.