Confused on next step

I worked the Sl Rib Pat until my piece is 19’’ from beg. Now I’m not sure how to proceed. The instructions say to work even until armholes measure 4 and then there is a Dec Row instruction below as well.

Row 2: P to first marker, work Row 2 of Sl Rib Pat to last marker, p to end. Work even in pat as established until piece measures 19(19-19½-19½-20-20)" from beg, end on WS. Mark beg and end of last row for beg of armholes. Work even until armholes measure 4(4-4½-4½-5-5½)", end on RS.

Dec Row (WS): P to first marker, drop marker, p to last marker, dec 13(11-13-11-13-11) sts as evenly spaced across as possible, drop marker, p to end - 72(82-90-100-108-118) sts. Work even in Garter St until armholes measure 8(8-8½-8½-9-9½)", end on WS. Mark center 28 sts on last row.

http://www.berroco.com/exclusives/pern/pern.html

When you’ve worked 19", place a marker at the beginning and end of the row. This can be as simple as a safety pin or a bit of scrap yarn which will mark the lower edge of the armhole. Continue on as you have been doing in pattern until you’re 4" from the markers at the lower edge of the armholes. On the next WS row, purl to the first pattern marker (this is different from the armhole markers), drop the marker, decrease 13 sts (or whatever is appropriate for the size you’re making) over the following center sts before the second marker, drop pattern marker 2 and purl to the end. Then you just continue in garter st over all the sts until the armholes measures 8".
Very nice patern which looks like fun to knit.

You’re doing the reverse of what you did before when you increased the sts, you decrease them now, evenly across the purl row. Then switch to garter stitch until it measures 8".