In many states, ambulances, firetrucks, etc, are exempt from emissions regulations. So depending on the location, it might be totally legal to delete the DPF. There are a number of good reasons to delete the DPF on an ambulance as well, depending on the drive cycles it sees. But I am with oscyjack, I am not sure it is necessary, as most of the time the emissions equipment works just fine.
If you are allowed to delete it, it should work just like on a pickup. Remove the parts, add in delete tubes / blocking plates, and flash a tune.