This is a rather unusual threadless stem setup. There is what is essentially a sleeve on the outside of the steerer tube that the stem can be adjusted up and down on, without juggling spacers. The sleeve itself is basically a large spacer. The stem and sleeve are made to work together; if you look closely you can see a raised ridge on the sleeve and a channel for the ridge on the stem (facing the front). It works pretty well for easy height adjustment. But again, the OP's stem is already at the highest point on the sleeve.