To rename a folder you must first click on it.  Once the page reloads and the folder is selected or highlighted; click on it a second time.  The folder name will appear in an edit window, go ahead and make your changes. Once you have made your changes, either hit the enter button on the keyboard or click somewhere else on the page.  This will cause the page to refresh and the folder to be renamed.  You should then see a message at the top of the screen detailing the outcome.