Update will not work

I have made several attempt to update Twenty Fourteen from 1.3 to 1.8, including adding 1.8 as a download. If I update from the themes page, i says it has updated but will not work… pages are blank and show an error message
Fatal error: Call to undefined function is_customize_preview() in /home/lestock/public_html/govt/wp-content/themes/twentyfourteen/inc/widgets.php on line 40

If I pload my dowloaded zip file, the update fails
What is the problem?