Make sure that you purchase all the clients and modules that you are using. Licenses are not currently node-locked, but you must have a license for each extension product that you plan to use. If you have the server license key, but do not have a license key for Oracle, for example, you will not be able to run Oracle backups with RMAN.
Generally speaking, the upgrade process consists of an uninstall and reinstall. Make sure to back up your catalog before an upgrade.