1) Go to the "games" menu and make sure it's there.
2) Read the brief instructions (use the pad to navigate, play to click and standby to exit)
3) Make sure it works (play one of the stations)

Ok, if you get this far, here's the very ugly part:

The station url and names are kept in a file:

/empeg/games/GrandCentral/etc/stations

You have to manually edit that file (probably have to ftp it off unless the central comes standard with an editor).