All your marketplace activity can be found in the "My Marketplace" selection under the "Marketplace" tab.
You will see a summary list of your current offers, sales, purchase as well as purchases and sales in Escrow and Escrow Arbitration requests.
To edit an offer, you can click on the offer ID. Every field can be edited and you can add or remove images.
When you are happy with your changes, click "Update Offers" -- ensure that your wallet is unlocked before you do this.
In the sales tab, you can see the offer details and buyers information.