See the screws on the side in the below picture? You need to loosen the screw with a screwdriver, slide the screw out, take the bracelet link(s) out, and then slide screw back in and tighten.
If this is your first time doing this, be careful of not letting the screwdriver head slip off the screwhead groove. If it does, you'll probably end up making a small scratch on the bracelet.
Cheers,
Anthony
