To change the hat size, just change your crochet hook size. The gauge provided is for hook size 5.5/ I , which is for a large size hat. If you want a XL then go up to a 6.5. And if you want a medium go down to a size 5.00mm/H hook. This hat is a basket weave stitch hat worked in the round from the top down.
Stitches: dc = double crochet
fpdc = front post double crochet
bpdc = back post double crochet
Less than 1 skein of yarn required to make a hat.