At this point you're working one shoulder of the sweater, leaving the other half for later.
So after you work the stitches, you turn the work as if you're done with the row and work back.
At the beginning of this partial row, you decreased at the armhole edge.
Continue on the last set of sts. as follows:- Dec 1 st as armhole edge as before on every following alternate row AT THE SAME TIME dec 1 st at neck edge on the next 4 rows, then on every following alt row until 8 sts remain.
So decrease at the armhole edge when the right side is facing you. (that will have you doing the decreases every other row)
ALSO, when you get to the neck edge in the center, decrease on the next 4 rows and every other
row after that until there are 8 stitches remaining.
Then you'll put the other half of the stitches on the needle and shape that side the same way.