These wristlets can easily be made smaller/bigger by adding/removing 4 stitches.

It isn’t necessary to change the thumb gusset if the hight of the rows is right, but I did notice in my own cabled version (which had a tighter gauge) that I had to stop increasing at 19 stitches, or it would be too wide. Just try as you go, you don’t have to increase untill the end. Just knit the gusset stitches untill you bind them off.