In what way are the arms too small? If the armhole is too short what I would do is to throw in a few more rows to make the yoke section longer. Since it has 1 row between increase rows, I would probably do 3 rows in a couple or three places. If you did only two the increases would be done on the opposite side from the others. If that isn’t a problem you could do 2 rows between the increases in more places evenly spaced from each other.
If the sleeves aren’t big enough around you need to somehow get more stitches in the total. You could increase a few more rounds just like you were doing in the regular instructions, that would make the armhole a little bigger and add a few stitches into each section. In effect it would make everything a little bigger, not just the arms.
Another thing you could do to gain just a little is to knit the sleeves in the round. When it tells you to work the sleeve flat and later sew it together, instead put the sleeve stitches on double points or however you’d like to work in the round. Right at the underarm part pick up some extra stitches, as many as you can get there as you join the sleeve to work it in the round.
Perhaps you could add extra increases into the sleeve sections of the yoke as you go down. I guess you could do that by adding increases on the usually non-increased rows, but only in the sleeve sections, right where they normally are when you increase the sleeves.