Does your theme have all this kind of information at the top of the stylesheet?
Theme Name: Yoko
Theme URI: http://www.elmastudio.de/wordpress-themes/yoko/
Description: Yoko is a modern three-column blog theme. A responsive layout optimizes the theme for mobile devices like tablet pcs and modern smartphones (the layout switches to a two- or one-column layout depending on the screen size the theme is viewed on). To make your blog post more flexible you can use different kinds of post formats such as gallery, image, video, aside, link or quotes. To customize the theme you can choose your own background, link color, logo and header image. Yoko also comes with a custom social links widget and shortcodes for text columns, info boxes and highlighted text.
Author URI: http://www.elmastudio.de/wordpress-themes/
Tags: light, three-columns, right-sidebar, flexible-width, custom-colors, custom-header, custom-background, custom-menu, theme-options, threaded-comments, sticky-post, translation-ready
License: GNU/GPL Version 2 or later
License URI: http://www.gnu.org/licenses/gpl.html
I've edited that information in the past and it's destroyed the theme, made it unusable. You need that information for some reason so make sure it exists.