After installing zencart, it defaults to the classic template.
Users are advised to create a CUSTOM template before they take their shops "live", and that's why you'll see many references to YOUR-TEMPLATE or CUSTOM-TEMPLATE in posts on this forum.
There are tutorials in the FAQ for how to create a custom template, and why it's important for OVER-RIDE purposes.
If you have not yet created a custom template, the button set being used will be in:-
/includes/templates/classic/buttons/english
It is NOT advisable to overwrite files in the classic template, as this template is very useful for site "de-bugging" purposes, so, go to the FAQ and find the tutorial about setting up a CUSTOM template.
Basically, when you navigate around the directory structure of your site, every "level" that contains a "classic" folder ought to have a CUSTOM folder as well - so, when you see a classic folder, just create another folder and name it with your CUSTOM template name. It does not matter if it's empty to start with. It gets used when you customise files.
So, for example, if you wanted to customise:
includes/templates/template_default/templates/tpl_product_info_display.php
... you would make changes, then store the edited file in:
includes/templates/YOUR-TEMPLATE/templates/tpl_product_info_display.php
When you have set up your CUSTOM template (you can give it any name you wish - as long as it's a sensible name for a directory set) you will CREATE folders along the way, in which to house customised files. This will include button sets.
