Postage prices, carrier information, and other data update automatically. You don't need to install anything for those.
Software updates depend on your operating system. On Linux, PostalPoint updates along with your computer's regular system updates. On Windows and Mac, PostalPoint notifies you when a new version is available; download the installer from the Download page and run it over your existing installation. Your data and settings are kept.
If you have multiple registers, update all of them at the same time so they stay on the same version. Registers running a different version than the database host PC will refuse to function until updated, in order to prevent database corruption.