restoring previous Navi versioin

How do you restore Navi to previous version if I don't like the new updated disk?
I saw this on a previous post(google}, but can't locate it. Something about holding in 3 buttons on the unit to reset.
Thanks

"MENU" + "MAP/GUIDE" + "Cancel" for 5 secs enters standard diagnostics mode. I can't remember but in one of the menus there's an option to reload.

Thanks.. Version comes up, press download and install disc.
Will also need Nav code.:)