Overriding virtuemart plugins

[dmb]

Joomla: 3.4.5
Virtuemart: 3.0.10

Hi,

I'm trying to change the layout of the page that appears when the shopper confirms the purchase (which in my case leads to Paypal).

I've followed the instructions on http://docs.virtuemart.net/tutorials/templating-layouts/101-how-to-overwrite-plugins.html which seem to do what I want, though it's not clear which versions of Virtuemart this applies to.

Specifically I've copied the directory plugins/vmpayment/paypal/paypal to templates/yoo_nano3/html/vmpayment/paypal and then changed the file vmpayment/helpers/paypalstd.php. However I don't see any effect on the live site, so I assume the override is not working and the default paypalstd.php is being used.

Anyone spot if I've made an error, or maybe if the method I'm using doesn't work with the version I've got ?

Thanks,

David