FAQ 7 used to mention that you can switch S1 styles on /modify.bml. This information is apparently not there any more; as far as I can see, it mentions selecting an S1 style only in the context of custom styles.
Perhaps add something like the following after the paragraph beginning "The Modify Journal page is also where you can input overrides"?
Finally, on the Modify Journal page, you can choose a style for your journal from one of LiveJournal's system styles.
or something like that.