I have 3 payment categories setup, these are existing from my first install but I've upgraded a few time since then now being on 4.2 (i think).
I don't see anywhere to add further categories so how to I change the existing ones. I've searched the database but they don't seem to now have their own table. I did find one of them in a table called cscart_original_values but god knows where the other two are. I only see them when adding a payment type.
Sorry to reply to my own post but I've now found them, I'll leave this up for others looking for what seems a massive fudge to me.
You'll find the categories in a table called "cscart_language_values"