The anchor posts can be found bolted to the inside of your timber panel frame. You can find them at the base on either end. To detach, you need to loosen the bolts and the anchor post will slide out. Turn upside-down and re-insert into frame aligning the holes in the anchor posts with the holes in the frame. Reattach with the loosened bolts to be ready for installation into ground.
See our installation page for a helpful guide on installing your letterbox.