I don't think that you can do that within the Windows UI
but you can find Registry entries for Windows Update in: "HKEY_LOCAL_MACHINE > SOFTWARE > Microsoft > Windows > CurrentVersion > WindowsUpdate".
My best guess (I have used the update only manually so I don't have a clue about the automatic update frequency) is that the "HistoricalSpeed" which is set at 216768 (roughly 60 hours) does control the frequency.
Just make sure that you backup (export) the Registry before editing it.