You need to look at the stitches on the row you are currently working on. Put the needle with the stitches on it in your left hand like you're going to start knitting the next row. Now, take a look at the first stitch and see if it's a knit stitch or a purl stitch. Does it look like a V or does it have a bump facing you??
If it looks like a V (a knit stitch) - then PURL that stitch. If it looks like a bump (a purl stitch) - then KNIT that stitch. Do the same for each stitch across the row. Because of the decreasing, this is one of those patterns where you are just going to have to "wing it" as you go!!!