A: Configuration Manager supports an in-place upgrade from System Center 2012 Configuration Manager 2012 to SP1. Launch the setup process from the SP1 media. The option to upgrade the existing site will be offered and selected by default. Prior to starting the upgrade, however, you should ensure the following requirements have been met:

During the upgrade all prerequisites will be checked, and assuming everything is in place, the upgrade of the site will complete without further user intervention.

A list of what is new in Configuration Manager 2012 SP1 can be found at the Microsoft article.  "What’s New in Configuration Manager SP1."