Using PowerShell
One advantage of PowerShell is that you can deploy changes to Windows Defender on multiple computers over the network.

If you prefer PowerShell way, follow the steps below:

Run PowerShell with administrative privileges (Windows key + X + A)
To disable real-time monitoring of Windows Defender, run the following command:
Set-MpPreference -DisableRealtimeMonitoring $true
To enable real-time monitoring, run the following command:
Set-MpPreference -DisableRealtimeMonitoring $false
The above method will only turn off real-time monitoring of Windows Defender. If you want to completely remove Windows Defender from Windows 10, use the following PowerShell command:

Uninstall-WindowsFeature -Name Windows-Defender