You change size in this pattern by changing yarn size and needle size (the information above is for size small). Here is the full yardage/needle size information for all sizes:

Women’s small (women’s medium/men’s small, women’s large /men’s medium, men’s large).

Fingering, sport, dk or worsted weight sock yarn, approximately 250 (200, 175, 150) yards.

US 2 (4, 6, 8) / 2.75 (3.5, 4, 5) mm or size needed to obtain gauge in circular or double point.

6.5 (5.5, 5, 4) stitches / 9 (7.5, 7, 5.5) rows per inch (2.5 cm) in 2 x 2 ribbing.