How to reduce the top and bottom margins of the side panel?

Please go to "Style Customizer > Others > Custom CSS" and use this custom CSS:

#side-container {
    padding-top: 20px;
}

#side-footer-wrapper {
    bottom: 20px;
}

You can adjust the px value here.

P.S. In case you would like to use custom CSS for other elements, I would recommend "Developer Tools" on Chrome or "Firebug" on Firefox to inspect the elements on the page. Then you can know which CSS selector to adjust.