How to change the ribbing on a garment to a folded edge.
If you are working from the bottom, cast on the number of stitches you are
instructed to with needles a size smaller than the body of the garment and in a
lighter weight yarn. Knit for about an inch and then purl one row.
Change to the larger needles and heavier weight yarn and continue up
the garment. To finish simply fold up the hem at the purl row and stitch
to the back of the garment. The purl row and the smaller needles
and yarn hold the hem down and in place.