You can manage, edit, and delete ads from the "Settings" control panel (upper right-hand of every page) and then scrolling down to the "My Classifieds" option located on the left-hand sidebar menu of this screen. From there you may edit, delete, close, or renew current and/or recently expired ads.
To update your pricing info, simply edit the ad you wish to keep and input a price, then save/submit those changes by clicking the corresponding button at the bottom of the page to commit your changes.