Poppy cowl is worked in the round from the bottom and up. To change the circumference, you can change your knitting tension/gauge. You can change tension/gauge by using a heavier yarn or with changing the needle size. Do remember that the cables will draw the work a bit together. Please note that by using another yarn the requirements may be different than those stated.

Pattern for Poppy Headband: Link

One size.
Circumference bottom 88 cm (35”).
Circumference top 54 cm (21”).
Length 24 cm (9 ½”).

Gauge after blocking:
Moss sts: 17 sts x 26 r = 10 x 10 cm (4”).
Pattern: 18,5 sts x 30 r = 10 x 10 cm (4”).

Tools:
Circular needle 4 mm/(US 6), 40 cm (16”).
Circular needle 4 mm/(US 6), 60 cm (24”).
Cable needle 4 mm/(US 6).
8 stitch marker.

Difficulty:
Intermediate.

Techniques:
Knit, purl, k-tbl, k2tog, p2tog, ssk, cable with k and p, 2-8 stitches.