I have purchased an extension to handle Australia Post postage but it can not work out which parcels will go as letters. I don't think there is a current extension that will.
I therefore need a text change in the delivery method part of the opencart program. Where it says "Please select the preferred shipping method to use on this order." I need to add some text to say if I can ship your order as a letter I will give a partial postage refund.
Does anyone know which file I need to modify to do this?