Hi charger70, you can open up the payment template file within /templates/admin/woocommerce-oc_store_checkout.php of our Plugin files. I notice we do not support Theme overrides but will include this in the next minor release.
Copy the woocommerce-oc_store_checkout.php file from that directory above to your current WordPress Theme directory (e.g. twenty-fourteen-child) and our Plugin will fetcth the payment template file from your Theme if it exists otherwise default to our original template file. 🙂
