Retro Portfolio (version 4) is not just a normal update but a new theme introducing new features to to give the users more powerful configuration options. So, if you are currently using a 3.X version or lower, please consider that migration to 4.X means to configure the theme from scratch.
Retina integration for logo and banner
Home Page customisation (you can easily add, remove and rearrange sections)
Colour options (you can easily change the colour of any single section, page or blog post thanks to the introduction of a new color picker)