Complex sentence: Then lines 1 thru 5 are changed to produce the first 6 hexagrams, then the fourth line of hexagram 6 is changed to produce hexagram 7, and changing the first three lines of hexagram 7 produces hexagram 8.
Split into simpler sentences: Then lines 1 thru 5 are changed to produce the first 6 hexagrams. Changing the first three lines of hexagram 7 produces hexagram 8.