For the purpose of straightening or rendering symmetrical the boundary or boundaries of any park or parkway owned by, or under the care, custody or control of, or laid out by it, the county park commission may dispose of and convey such portion of any real estate acquired for park purposes, as in its judgment may not be required for park purposes, in exchange for other real estate contiguous thereto, in area equal to, or greater than, the real estate to be conveyed by it.