I have been terrible afraid of updating my Unite Theme as I do not know if I will lose all my customization that we have added. I currently have version 1.6.1 installed and I know the most current version is 2.0.2. How do I know if I choose to update the most current version, I will NOT lose any of the customization we have added?
I think that in order to save all your customization and not to worry when your are updating your theme you have to create and activate a child theme on your wordpress installation
A WordPress child theme is a WordPress theme that inherits its functionality from another WordPress theme, the parent theme. Child themes are often used when you want to customize or tweak an existing WordPress theme without losing the ability to upgrade that theme
See in attach a doc that explains you how to make a child theme.
All the css custom you could copy in the style css of the child theme.