TOC Related questions

Hello Everyone,

I have recently tried to generate a TOC in word 2010. Only problem is that I want to use my own custom styles instead of those 

TOC1, TOC2, ....... etc.

I noticed that if I go to:

reference Tab >> Table Of Contents >> Insert Table of Contents >> modify button

a new dialog with a title of: Style opens up, in it there are two disabled buttons:New and Delete, I am guessing that these are the buttons that will allow me to do exactly what I want, except that the two buttons areDisabled.

Does anyone know why these buttons are disabled and better yet, what do I need to do in order to enable them?

Any help would be very much appreciated

Best Regards,