Well that's weird. I'm not sure how to "Decrease either side every other row once ". To do something "once" makes it impossible to do it "every other row". :?? But here's my guess...
Row 1 - decrease on both sides.
Row 2 - work even
Row 3 - work even
Row 4 - work even
Row 5 - decrease on both sides.
Repeat row 1-5 9 times.