To made the hat slightly bigger or smaller, you can CO more or fewer stitches for the stockinette section.

ETA In the pattern I said to CO 30, then K2P2 to the end. Of course that leaves you with 2 extra stitches. Please K2P2 until you have 2 sts remaining, then K1P1.. I will try to update the PDF asap. Thanks for your patience.