DVD video edition again.

[Strong]

I've posted the message but thought i lost Your precious answers, yet i
didn't find it in archive too, so, i'll try to repeat again my questions
on this subject.
I want to edit a DVD movie (video and sound) yet let's look on it in two
ways:
a) video and sound; b) sound only, if it helps to save quality somehow.
So, How to make it the best (the easiest)?
Probably i need to unpack > edit > pack DVD again. - By what. Is there a
way to spare quality if i edit one sound track only? Can i delete a
track?
Thank You for participation! - It's a big deal to me!

-- 
Best regards,
Strong.