How to Disable Theme Changing in the WordPress Dashboard

Don’t want clients messing around with themes on their site?

If you want to keep your WordPress theme set as it is and make sure that your client is not able to experiment with theme changes, add this to your functions.php file:

add_action('admin_init', 'remove_theme_menus');
function remove_theme_menus() {
global $submenu;
unset($submenu['themes.php'][5]);
unset($submenu['themes.php'][15]);
}

This snippet will remove Themes from the Dashboard >> Appearance menu.

Source: WPTricks.net