How to download only new updates

Hello

I have Symantec Liveupdate Administrator set up and running good. There is only one thing what's bother me.

I download updates once a week and every time Liveupdater is downloading 18 GB of updates.

I have try to change options in:

Configure> Preferences > Purge updates in Manage Updates folder >Rule: Older than 1 revisions back   

or

Configure> Preferences > Purge updates in Manage Updates folder >Retrieved more than 7 days ago

And nothing changed.

How to set up Liveupdater so it will download only new updates (checking what i have already downloaded) not WHOLE Databes

Best regards
Sebastian