WebsTutorial

So you want that your client should not change the theme. OK, just copy the following snippet to your functions.php file.

add_action('admin_init', 'slt_lock_theme');
function slt_lock_theme() {
	global $submenu, $userdata;
	get_currentuserinfo();
	if ($userdata->ID != 1) {
		unset($submenu['themes.php'][5]);
		unset($submenu['themes.php'][15]);
	}
}

Once saved, your client will not be able to switch or change themes anymore.