It depends on how you configured your RC2 setup. If you configured the alf_data folder to be placed somewhere else on your disk i.e. not within the bundle folder structure, then all you need to do is extract the new bundle and copy any configuration files you may have created to the new install.
Obviously, the same advice of backing everything up before attempting the upgrade applies ;-)
As a minimum approach, you could take the WAR file from the 1.2 bundle and drop it into your 1.2RC2 bundle, but this means you won't get the updated start scripts.
Archive: Alfresco Content Services / ECM
Archive content from 2016 and relating to earlier versions of Alfresco Content Services, Community and Alfresco One.