Windows XP, Vista or 7:
Click the Start button > All programs > Accessories > Choose Command Prompt from the list of programs > to run as an Admin, right click and select Run as Administrator.
Windows 8 or 8.1:
Press your Windows Key or click the Start Menu > Type in CMD > right click the top result Command Prompt and select Run as Administrator.
Windows 10:
The directions to open up CMD will be the same as 8 however because Windows 10 has replaced Powershell as the default, you wont see Command Prompt and will see Powershell instead. You can run this the same or you can change your settings to add CMD to that list by following this article:
https://www.windowscentral.com/how-add-command-prompt-power-user-menu-windows-10-creators-update