Put on work gloves and dig around the support posts, making a hole at least 2 feet deep by 1 foot wide to expose the concrete footing.
Put on safety glasses and plug in an electric jackhammer. Set the jackhammer chisel directly onto the concrete footer and begin to break it up. Chisel away the concrete footing, breaking off large pieces of concrete around the support post.
Pause periodically, shut off the jackhammer and pull out loose pieces of the concrete footing, setting them aside.
Continue to break up the concrete footing with the jackhammer until the support post comes free. Then remove all the loose concrete pieces from the hole and back-fill the hole with the excavated dirt to finish.