You can do this in three ways:
1st method: Simply right-click on the New tab extension icon from the toolbar, in the upper right part of the browser, and click on “Remove from Chrome”.
2st method: Another option is to click on the menu icon, on the upper right part of the screen, and click on Settings. On the appeared menu, select “Extensions” When you find the extension you want to remove, click on the trash bin icon and it will be removed immediately!
3st method: If you want to remove the theme, please follow the instructions below. Or you can go to “chrome://extensions”, find the extensions you want to remove and click the “Trash” icon.