How to change text on Drupal WorldPay button?
In this specific case, you can implement hook_commerce_payment_method_info_alter(&amp;$payment_methods) in a custom module, and alter $payment_methods['commerce_worldpay_bg']['title'].

If you see other instances of the strings, which aren't changed, then you can use the String Overrides module, as already suggested, or use the $conf global variable in settings.php as follows.

$conf['locale_custom_strings_en'][''] = array(
  'Payment via Worldpay' =&gt; 'Your string',
);


Keep in mind that the latter two methods change the string wherever it is used; they don't provide a context to understand where the string is being used. This could be something you want, or not.