Register form changing

Hello. I created a shop on opencart cms, and I want to change the register form from guest checkout and register.
from admincp, I can't delete some fields which are requested, but I don't need them because my shop is a digital delivery based shop, so I don't need his address, telephone and thinks like that.
Can someone help me and give me the name of all files which include:
Form itself, database queue (want to modify tables and also remove some items from queue because I want to remote that fields, not just hide them) and all files related to address, telephone and so on, because if I remove this tables, I don't want to cause some errors to cms.
Thanks.

I need that database modification so it would be easier to my to work with it (to allow login to my forum with shop user/pass).

many pages on info about this:
https://www.google.ch/search?q=hide+reg ... 0+opencart
Ernie
bigmax.ch/os/