Moosh wrote:
My site is based in the UK. On registration I want to change the name of the the Zip code field to Postcode.
Which file do I edit?
Thanks in advance.

Assuming you have used the CB Tools -> Load Sample Data option the the CB backend to add this field to begin with.
By clicking this link a number of fields are automatically created for you - you can see these in the CB Fields Management backend.
One of these fields is the zipcode field you must be referring to. If you edit this field by clicking it in the CB Fields management area you will see that the title of the field is set to _UE_ZipCode.
You have 2 options - if your site is a single language site you can either just over-write this value with whatever you want (e.g. Postcode) or you can find the default_language.php file (look in your component->com_profiler->plugin->language->default_language folder) and edit the _UE_ZipCode string.
If you have a multi-language site (or single language other than English) you should find the relevant language files (similar location) and edit the string(s) there.
Really simple once you understand whats happening.