My DB is similar to a shop DB, and i'm changing from "selling" items with a unique product code to one which doesn't require a product code. Instead there will be a set quantity of the products.

How would i make this change?

It's hard to say because the details of what you're trying do are absent.

Ok, well its the DB is loaning out items (similar to a library). And previously to loan out an item, its product code would be entered into user's portal, then issued to that user. However now, the items being issued do not have an individual product code.

So instead of eg. Item number "IO234" being issued to a user, now a "shirt" will be issued (for which there are many, eg. 20).

I'm guessing this is a similar setup for a shop...Hope this is clear enough

I guess, instead of asking what changes need to be made, but how does it need to be setup?

This thread might get you started:

http://fmforums.com/forum/showtopic.php?tid/168633