Posts Not Set In Concrete
If the post is not in concrete, you should be able to loosen it by rocking it back and forth so you can pull it out by hand. Gloves can aid in giving a better group and also prevent splinters.
Posts Set In Concrete
If the post is set in concrete, loosening it by hand will probably not be an option. Take a shovel and loosen all of the dirt around the slab. Keep removing the dirt so that the entire top of the concrete is exposed.
Next, wrap a log chain around the concrete, do this in one strand and just under the lip. Secure the chain in place by hooking one end to itself. Now set the jack by the post. Take the other end of the chain and wrap it on the jack foot. Now use one hand to pump the jack handle and hold the chain in place with your other hand, which will create tension. Keep pumping until the post is out of the ground. Prepare for a significant amount of energy, especially just before the post lifts.
Tearing Down A Chain Link Fence