how can i edit or change the equipment items for normal characters original sets

This is done in create a character mode,

First choose a character you want to edit, for example

I want equip the Soul Calibur to Cassandra, so I go to create a character mode, a select Cassandra,
next I choose a look for her, you can choose the default outfits each character has or you can make your own,
and finally you can choose what weapon to give your character, so in my case I equip Cassandra with the Soul Calibur.

I wouldn't equip anything with the bonus characters because I tried that with Shura one time and it really wasn't any different than her defaut weapon and bonus characters can't have there outfits changed.

I hope this helps.