Moving or replacing a mailbox requires removing the existing box. Most mailbox posts insert into the ground with poured concrete. The concrete provides some stability for the mailbox post. If you want to reuse the existing post or just make it easier to dispose of, the concrete requires removal. Removing concrete from a mailbox post is a matter of breaking the concrete by force.
Dig around the mailbox post with a shovel. Dig 6 inches out from the edge of the concrete and as deep as the concrete. Ask a friend to rock the mailbox post back and forth to loosen the concrete from the ground.
Lift the mailbox post out of the ground with the help of your assistant. Mailbox posts usually have only enough concrete to set the pole, unlike fence posts, which require more stability.
Lay the mailbox post flat on the ground. Hold the blade of a cold chisel on the side of the concrete that is facing you. Hit the top of the chisel with a hand sledgehammer. This begins to crack the concrete in chunks.
Continue removing the concrete with the cold chisel and hammer until one side of the mailbox post is free. Position the chisel at the exposed seam between the concrete and mailbox post. Hit the top of the chisel to continue breaking up the concrete.
Turn the mailbox post over as necessary to chisel away the concrete.